diff --git a/docs/authentication.rst b/docs/authentication.rst
index 11e3f31e..b38468d6 100644
--- a/docs/authentication.rst
+++ b/docs/authentication.rst
@@ -54,6 +54,9 @@ or an instance of :class:`kopf.ConnectionInfo`::
             expiration=datetime.datetime(2099, 12, 31, 23, 59, 59),
         )
 
+Both TZ-naive & TZ-aware expiration times are supported.
+The TZ-naive timestamps are always treated as UTC.
+
 As with any other handlers, the login handler can be async if the network
 communication is needed and async mode is supported::
 
diff --git a/docs/errors.rst b/docs/errors.rst
index 784e30e3..1139cc4f 100644
--- a/docs/errors.rst
+++ b/docs/errors.rst
@@ -56,7 +56,7 @@ is no need to retry over time, as it will not become better::
     @kopf.on.create('kopfexamples')
     def create_fn(spec, **_):
         valid_until = datetime.datetime.fromisoformat(spec['validUntil'])
-        if valid_until <= datetime.datetime.utcnow():
+        if valid_until <= datetime.datetime.now(datetime.timezone.utc):
             raise kopf.PermanentError("The object is not valid anymore.")
 
 See also: :ref:`never-again-filters` to prevent handlers from being invoked
diff --git a/docs/probing.rst b/docs/probing.rst
index 601ad40a..c7a92819 100644
--- a/docs/probing.rst
+++ b/docs/probing.rst
@@ -76,7 +76,7 @@ probing handlers:
 
     @kopf.on.probe(id='now')
     def get_current_timestamp(**kwargs):
-        return datetime.datetime.utcnow().isoformat()
+        return datetime.datetime.now(datetime.timezone.utc).isoformat()
 
     @kopf.on.probe(id='random')
     def get_random_value(**kwargs):
@@ -91,7 +91,7 @@ The handler results will be reported as the content of the liveness response:
 .. code-block:: console
 
     $ curl http://localhost:8080/healthz
-    {"now": "2019-11-07T18:03:52.513803", "random": 765846}
+    {"now": "2019-11-07T18:03:52.513803+00:00", "random": 765846}
 
 .. note::
     The liveness status report is simplistic and minimalistic at the moment.
diff --git a/examples/13-hooks/example.py b/examples/13-hooks/example.py
index 3bd66466..2f44c194 100644
--- a/examples/13-hooks/example.py
+++ b/examples/13-hooks/example.py
@@ -55,7 +55,7 @@ async def login_fn(**kwargs):
         certificate_path=cert.filename() if cert else None,  # can be a temporary file
         private_key_path=pkey.filename() if pkey else None,  # can be a temporary file
         default_namespace=config.namespace,
-        expiration=datetime.datetime.utcnow() + datetime.timedelta(seconds=30),
+        expiration=datetime.datetime.now(datetime.timezone.utc) + datetime.timedelta(seconds=30),
     )
 
 
diff --git a/kopf/_cogs/clients/events.py b/kopf/_cogs/clients/events.py
index 3bca4bb6..3742f863 100644
--- a/kopf/_cogs/clients/events.py
+++ b/kopf/_cogs/clients/events.py
@@ -49,7 +49,7 @@ async def post_event(
         suffix = message[-MAX_MESSAGE_LENGTH // 2 + (len(infix) - len(infix) // 2):]
         message = f'{prefix}{infix}{suffix}'
 
-    now = datetime.datetime.utcnow()
+    now = datetime.datetime.now(datetime.timezone.utc)
     body = {
         'metadata': {
             'namespace': namespace,
@@ -67,9 +67,9 @@ async def post_event(
 
         'involvedObject': full_ref,
 
-        'firstTimestamp': now.isoformat() + 'Z',  # '2019-01-28T18:25:03.000000Z' -- seen in `kubectl describe ...`
-        'lastTimestamp': now.isoformat() + 'Z',  # '2019-01-28T18:25:03.000000Z' - seen in `kubectl get events`
-        'eventTime': now.isoformat() + 'Z',  # '2019-01-28T18:25:03.000000Z'
+        'firstTimestamp': now.isoformat(),  # seen in `kubectl describe ...`
+        'lastTimestamp': now.isoformat(),  # seen in `kubectl get events`
+        'eventTime': now.isoformat(),
     }
 
     try:
diff --git a/kopf/_cogs/structs/credentials.py b/kopf/_cogs/structs/credentials.py
index 9a40bb3f..cba84467 100644
--- a/kopf/_cogs/structs/credentials.py
+++ b/kopf/_cogs/structs/credentials.py
@@ -61,7 +61,7 @@ class ConnectionInfo:
     private_key_data: Optional[bytes] = None
     default_namespace: Optional[str] = None  # used for cluster objects' k8s-events.
     priority: int = 0
-    expiration: Optional[datetime.datetime] = None  # TZ-naive, the same as utcnow()
+    expiration: Optional[datetime.datetime] = None  # TZ-aware or TZ-naive (implies UTC)
 
 
 _T = TypeVar('_T', bound=object)
@@ -118,7 +118,7 @@ def __init__(
         self._current = {}
         self._invalid = collections.defaultdict(list)
         self._lock = asyncio.Lock()
-        self._next_expiration = datetime.datetime.max
+        self._next_expiration: Optional[datetime.datetime] = None
 
         if __src is not None:
             self._update_converted(__src)
@@ -229,13 +229,19 @@ async def expire(self) -> None:
         Unlike invalidation, the expired credentials are not remembered
         and not blocked from reappearing.
         """
-        now = datetime.datetime.utcnow()
-        if now >= self._next_expiration:  # quick & lockless for speed: it is done on every API call
+        now = datetime.datetime.now(datetime.timezone.utc)
+
+        # Quick & lockless for speed: it is done on every API call, we have no time for locks.
+        if self._next_expiration is not None and now >= self._next_expiration:
             async with self._lock:
                 for key, item in list(self._current.items()):
-                    if item.info.expiration is not None and now >= item.info.expiration:
-                        await self._flush_caches(item)
-                        del self._current[key]
+                    expiration = item.info.expiration
+                    if expiration is not None:
+                        if expiration.tzinfo is None:
+                            expiration = expiration.replace(tzinfo=datetime.timezone.utc)
+                        if now >= expiration:
+                            await self._flush_caches(item)
+                            del self._current[key]
                 self._update_expiration()
                 need_reauth = not self._current  # i.e. nothing is left at all
 
@@ -315,11 +321,12 @@ async def populate(
         await self._ready.turn_to(True)
 
     def is_empty(self) -> bool:
-        now = datetime.datetime.utcnow()
-        return all(
-            item.info.expiration is not None and now >= item.info.expiration  # i.e. expired
-            for key, item in self._current.items()
-        )
+        now = datetime.datetime.now(datetime.timezone.utc)
+        expirations = [
+            dt if dt is None or dt.tzinfo is not None else dt.replace(tzinfo=datetime.timezone.utc)
+            for dt in (item.info.expiration for item in self._current.values())
+        ]
+        return all(dt is not None and now >= dt for dt in expirations)  # i.e. expired
 
     async def wait_for_readiness(self) -> None:
         await self._ready.wait_for(True)
@@ -381,8 +388,8 @@ def _update_converted(
 
     def _update_expiration(self) -> None:
         expirations = [
-            item.info.expiration
-            for item in self._current.values()
-            if item.info.expiration is not None
+            dt if dt.tzinfo is not None else dt.replace(tzinfo=datetime.timezone.utc)
+            for dt in (item.info.expiration for item in self._current.values())
+            if dt is not None
         ]
-        self._next_expiration = min(expirations + [datetime.datetime.max])
+        self._next_expiration = min(expirations) if expirations else None
diff --git a/kopf/_core/actions/application.py b/kopf/_core/actions/application.py
index 805dda23..22f8e99b 100644
--- a/kopf/_core/actions/application.py
+++ b/kopf/_core/actions/application.py
@@ -89,7 +89,7 @@ async def apply(
             logger.debug(f"Sleeping was interrupted by new changes, {unslept_delay} seconds left.")
         else:
             # Any unique always-changing value will work; not necessary a timestamp.
-            value = datetime.datetime.utcnow().isoformat()
+            value = datetime.datetime.now(datetime.timezone.utc).isoformat()
             touch = patches.Patch()
             settings.persistence.progress_storage.touch(body=body, patch=touch, value=value)
             await patch_and_check(
diff --git a/kopf/_core/actions/execution.py b/kopf/_core/actions/execution.py
index 37573f69..89cb095c 100644
--- a/kopf/_core/actions/execution.py
+++ b/kopf/_core/actions/execution.py
@@ -113,7 +113,7 @@ def finished(self) -> bool:
     @property
     def sleeping(self) -> bool:
         ts = self.delayed
-        now = datetime.datetime.utcnow()
+        now = datetime.datetime.now(datetime.timezone.utc)
         return not self.finished and ts is not None and ts > now
 
     @property
@@ -122,7 +122,7 @@ def awakened(self) -> bool:
 
     @property
     def runtime(self) -> datetime.timedelta:
-        now = datetime.datetime.utcnow()
+        now = datetime.datetime.now(datetime.timezone.utc)
         return now - (self.started if self.started else now)
 
 
@@ -277,7 +277,7 @@ async def execute_handler_once(
             handler=handler,
             cause=cause,
             retry=state.retries,
-            started=state.started or datetime.datetime.utcnow(),  # "or" is for type-checking.
+            started=state.started or datetime.datetime.now(datetime.timezone.utc),  # "or" is for type-checking.
             runtime=state.runtime,
             settings=settings,
             lifecycle=lifecycle,  # just a default for the sub-handlers, not used directly.
diff --git a/kopf/_core/actions/progression.py b/kopf/_core/actions/progression.py
index 65367ee5..337d2998 100644
--- a/kopf/_core/actions/progression.py
+++ b/kopf/_core/actions/progression.py
@@ -18,6 +18,8 @@
 from typing import Any, Collection, Dict, Iterable, Iterator, \
                    Mapping, NamedTuple, Optional, overload
 
+import iso8601
+
 from kopf._cogs.configs import progress
 from kopf._cogs.structs import bodies, ids, patches
 from kopf._core.actions import execution
@@ -54,7 +56,7 @@ class HandlerState(execution.HandlerState):
     def from_scratch(cls, *, purpose: Optional[str] = None) -> "HandlerState":
         return cls(
             active=True,
-            started=datetime.datetime.utcnow(),
+            started=datetime.datetime.now(datetime.timezone.utc),
             purpose=purpose,
         )
 
@@ -62,9 +64,9 @@ def from_scratch(cls, *, purpose: Optional[str] = None) -> "HandlerState":
     def from_storage(cls, __d: progress.ProgressRecord) -> "HandlerState":
         return cls(
             active=False,
-            started=_datetime_fromisoformat(__d.get('started')) or datetime.datetime.utcnow(),
-            stopped=_datetime_fromisoformat(__d.get('stopped')),
-            delayed=_datetime_fromisoformat(__d.get('delayed')),
+            started=_parse_iso8601(__d.get('started')) or datetime.datetime.now(datetime.timezone.utc),
+            stopped=_parse_iso8601(__d.get('stopped')),
+            delayed=_parse_iso8601(__d.get('delayed')),
             purpose=__d.get('purpose') if __d.get('purpose') else None,
             retries=__d.get('retries') or 0,
             success=__d.get('success') or False,
@@ -76,9 +78,9 @@ def from_storage(cls, __d: progress.ProgressRecord) -> "HandlerState":
 
     def for_storage(self) -> progress.ProgressRecord:
         return progress.ProgressRecord(
-            started=None if self.started is None else _datetime_toisoformat(self.started),
-            stopped=None if self.stopped is None else _datetime_toisoformat(self.stopped),
-            delayed=None if self.delayed is None else _datetime_toisoformat(self.delayed),
+            started=None if self.started is None else _format_iso8601(self.started),
+            stopped=None if self.stopped is None else _format_iso8601(self.stopped),
+            delayed=None if self.delayed is None else _format_iso8601(self.delayed),
             purpose=None if self.purpose is None else str(self.purpose),
             retries=None if self.retries is None else int(self.retries),
             success=None if self.success is None else bool(self.success),
@@ -104,7 +106,7 @@ def with_outcome(
             self,
             outcome: execution.Outcome,
     ) -> "HandlerState":
-        now = datetime.datetime.utcnow()
+        now = datetime.datetime.now(datetime.timezone.utc)
         cls = type(self)
         return cls(
             active=self.active,
@@ -313,7 +315,7 @@ def delays(self) -> Collection[float]:
         processing routine, based on all delays of different origin:
         e.g. postponed daemons, stopping daemons, temporarily failed handlers.
         """
-        now = datetime.datetime.utcnow()
+        now = datetime.datetime.now(datetime.timezone.utc)
         return [
             max(0, (handler_state.delayed - now).total_seconds()) if handler_state.delayed else 0
             for handler_state in self._states.values()
@@ -355,30 +357,24 @@ def deliver_results(
 
 
 @overload
-def _datetime_toisoformat(val: None) -> None: ...
+def _format_iso8601(val: None) -> None: ...
 
 
 @overload
-def _datetime_toisoformat(val: datetime.datetime) -> str: ...
+def _format_iso8601(val: datetime.datetime) -> str: ...
 
 
-def _datetime_toisoformat(val: Optional[datetime.datetime]) -> Optional[str]:
-    if val is None:
-        return None
-    else:
-        return val.isoformat(timespec='microseconds')
+def _format_iso8601(val: Optional[datetime.datetime]) -> Optional[str]:
+    return None if val is None else val.isoformat(timespec='microseconds')
 
 
 @overload
-def _datetime_fromisoformat(val: None) -> None: ...
+def _parse_iso8601(val: None) -> None: ...
 
 
 @overload
-def _datetime_fromisoformat(val: str) -> datetime.datetime: ...
+def _parse_iso8601(val: str) -> datetime.datetime: ...
 
 
-def _datetime_fromisoformat(val: Optional[str]) -> Optional[datetime.datetime]:
-    if val is None:
-        return None
-    else:
-        return datetime.datetime.fromisoformat(val)
+def _parse_iso8601(val: Optional[str]) -> Optional[datetime.datetime]:
+    return None if val is None else iso8601.parse_date(val)  # always TZ-aware
diff --git a/kopf/_core/engines/peering.py b/kopf/_core/engines/peering.py
index 6c511f8e..75f66502 100644
--- a/kopf/_core/engines/peering.py
+++ b/kopf/_core/engines/peering.py
@@ -68,10 +68,9 @@ def __init__(
         self.priority = priority
         self.lifetime = datetime.timedelta(seconds=int(lifetime))
         self.lastseen = (iso8601.parse_date(lastseen) if lastseen is not None else
-                         datetime.datetime.utcnow())
-        self.lastseen = self.lastseen.replace(tzinfo=None)  # only the naive utc -- for comparison
+                         datetime.datetime.now(datetime.timezone.utc))
         self.deadline = self.lastseen + self.lifetime
-        self.is_dead = self.deadline <= datetime.datetime.utcnow()
+        self.is_dead = self.deadline <= datetime.datetime.now(datetime.timezone.utc)
 
     def __repr__(self) -> str:
         clsname = self.__class__.__name__
@@ -149,7 +148,7 @@ async def process_peering_event(
     # are expected to expire, and force the immediate re-evaluation by a certain change of self.
     # This incurs an extra PATCH request besides usual keepalives, but in the complete silence
     # from other peers that existed a moment earlier, this should not be a problem.
-    now = datetime.datetime.utcnow()
+    now = datetime.datetime.now(datetime.timezone.utc)
     delays = [(peer.deadline - now).total_seconds() for peer in same_peers + prio_peers]
     unslept = await aiotime.sleep(delays, wakeup=stream_pressure)
     if unslept is None and delays:
@@ -279,7 +278,7 @@ def detect_own_id(*, manual: bool) -> Identity:
 
     user = getpass.getuser()
     host = hostnames.get_descriptive_hostname()
-    now = datetime.datetime.utcnow().strftime("%Y%m%d%H%M%S")
+    now = datetime.datetime.now(datetime.timezone.utc).strftime("%Y%m%d%H%M%S")
     rnd = ''.join(random.choices('abcdefhijklmnopqrstuvwxyz0123456789', k=3))
     return Identity(f'{user}@{host}' if manual else f'{user}@{host}/{now}/{rnd}')
 
diff --git a/kopf/_core/engines/probing.py b/kopf/_core/engines/probing.py
index 51675a46..0c1bbb99 100644
--- a/kopf/_core/engines/probing.py
+++ b/kopf/_core/engines/probing.py
@@ -48,10 +48,10 @@ async def get_health(
 
         # Recollect the data on-demand, and only if is is older that a reasonable caching period.
         # Protect against multiple parallel requests performing the same heavy activity.
-        now = datetime.datetime.utcnow()
+        now = datetime.datetime.now(datetime.timezone.utc)
         if probing_timestamp is None or now - probing_timestamp >= probing_max_age:
             async with probing_lock:
-                now = datetime.datetime.utcnow()
+                now = datetime.datetime.now(datetime.timezone.utc)
                 if probing_timestamp is None or now - probing_timestamp >= probing_max_age:
 
                     activity_results = await activities.run_activity(
@@ -64,7 +64,7 @@ async def get_health(
                     )
                     probing_container.clear()
                     probing_container.update(activity_results)
-                    probing_timestamp = datetime.datetime.utcnow()
+                    probing_timestamp = datetime.datetime.now(datetime.timezone.utc)
 
         return aiohttp.web.json_response(probing_container)
 
diff --git a/tests/authentication/test_vault.py b/tests/authentication/test_vault.py
index fa099cac..38da0043 100644
--- a/tests/authentication/test_vault.py
+++ b/tests/authentication/test_vault.py
@@ -1,6 +1,7 @@
 import datetime
 
 import freezegun
+import iso8601
 import pytest
 
 from kopf._cogs.structs.credentials import ConnectionInfo, LoginError, Vault, VaultKey
@@ -55,7 +56,7 @@ async def test_yielding_after_population(mocker):
 
 @freezegun.freeze_time('2020-01-01T00:00:00')
 async def test_yielding_items_before_expiration(mocker):
-    future = datetime.datetime(2020, 1, 1, 0, 0, 0, 1)
+    future = iso8601.parse_date('2020-01-01T00:00:00.000001')
     key1 = VaultKey('some-key')
     info1 = ConnectionInfo(server='https://expected/', expiration=future)
     vault = Vault()
@@ -74,8 +75,8 @@ async def test_yielding_items_before_expiration(mocker):
 @pytest.mark.parametrize('delta', [0, 1])
 @freezegun.freeze_time('2020-01-01T00:00:00')
 async def test_yielding_ignores_expired_items(mocker, delta):
-    future = datetime.datetime(2020, 1, 1, 0, 0, 0, 1)
-    past = datetime.datetime(2020, 1, 1) - datetime.timedelta(microseconds=delta)
+    future = iso8601.parse_date('2020-01-01T00:00:00.000001')
+    past = iso8601.parse_date('2020-01-01') - datetime.timedelta(microseconds=delta)
     key1 = VaultKey('some-key')
     key2 = VaultKey('other-key')
     info1 = ConnectionInfo(server='https://expected/', expiration=past)
@@ -96,7 +97,7 @@ async def test_yielding_ignores_expired_items(mocker, delta):
 @pytest.mark.parametrize('delta', [0, 1])
 @freezegun.freeze_time('2020-01-01T00:00:00')
 async def test_yielding_when_everything_is_expired(mocker, delta):
-    past = datetime.datetime(2020, 1, 1) - datetime.timedelta(microseconds=delta)
+    past = iso8601.parse_date('2020-01-01') - datetime.timedelta(microseconds=delta)
     key1 = VaultKey('some-key')
     info1 = ConnectionInfo(server='https://expected/', expiration=past)
     vault = Vault()
diff --git a/tests/handling/daemons/conftest.py b/tests/handling/daemons/conftest.py
index bdd0f846..fc6f2ae5 100644
--- a/tests/handling/daemons/conftest.py
+++ b/tests/handling/daemons/conftest.py
@@ -104,7 +104,7 @@ def frozen_time():
     A helper to simulate time movements to step over long sleeps/timeouts.
     """
     # TODO LATER: Either freezegun should support the system clock, or find something else.
-    with freezegun.freeze_time("2020-01-01 00:00:00") as frozen:
+    with freezegun.freeze_time("2020-01-01T00:00:00") as frozen:
         # Use freezegun-supported time instead of system clocks -- for testing purposes only.
         # NB: Patch strictly after the time is frozen -- to use fake_time(), not real time().
         with patch('time.monotonic', time.time), patch('time.perf_counter', time.time):
diff --git a/tests/handling/indexing/test_index_exclusion.py b/tests/handling/indexing/test_index_exclusion.py
index f015613e..1deeb58d 100644
--- a/tests/handling/indexing/test_index_exclusion.py
+++ b/tests/handling/indexing/test_index_exclusion.py
@@ -1,8 +1,8 @@
 import asyncio
-import datetime
 import logging
 
 import freezegun
+import iso8601
 import pytest
 
 from kopf._cogs.aiokits.aiotoggles import Toggle
@@ -76,7 +76,7 @@ async def test_temporary_failures_with_expired_delays_are_reindexed(
         resource, namespace, settings, registry, memories, indexers, index, caplog, event_type, handlers):
     caplog.set_level(logging.DEBUG)
     body = {'metadata': {'namespace': namespace, 'name': 'name1'}}
-    delayed = datetime.datetime(2020, 12, 31, 23, 59, 59, 0)
+    delayed = iso8601.parse_date('2020-12-31T23:59:59')
     memory = await memories.recall(raw_body=body)
     memory.indexing_memory.indexing_state = State({'index_fn': HandlerState(delayed=delayed)})
     await process_resource_event(
@@ -153,9 +153,9 @@ async def test_removed_and_remembered_on_permanent_errors(
 
 @freezegun.freeze_time('2020-12-31T00:00:00')
 @pytest.mark.parametrize('delay_kwargs, expected_delayed', [
-    (dict(), datetime.datetime(2020, 12, 31, 0, 1, 0)),
-    (dict(delay=0), datetime.datetime(2020, 12, 31, 0, 0, 0)),
-    (dict(delay=9), datetime.datetime(2020, 12, 31, 0, 0, 9)),
+    (dict(), iso8601.parse_date('2020-12-31T00:01:00')),
+    (dict(delay=0), iso8601.parse_date('2020-12-31T00:00:00')),
+    (dict(delay=9), iso8601.parse_date('2020-12-31T00:00:09')),
     (dict(delay=None), None),
 ])
 @pytest.mark.usefixtures('indexed_123')
diff --git a/tests/handling/test_cause_logging.py b/tests/handling/test_cause_logging.py
index b6ca44bb..f6a673d0 100644
--- a/tests/handling/test_cause_logging.py
+++ b/tests/handling/test_cause_logging.py
@@ -1,8 +1,8 @@
 import asyncio
-import datetime
 import logging
 
 import freezegun
+import iso8601
 import pytest
 
 import kopf
@@ -106,7 +106,7 @@ async def test_diffs_not_logged_if_absent(registry, settings, resource, handlers
 
 
 # Timestamps: time zero (0), before (B), after (A), and time zero+1s (1).
-TS0 = datetime.datetime(2020, 12, 31, 23, 59, 59, 123456)
+TS0 = iso8601.parse_date('2020-12-31T23:59:59.123456')
 TS1_ISO = '2021-01-01T00:00:00.123456'
 
 
diff --git a/tests/handling/test_delays.py b/tests/handling/test_delays.py
index 3b00dd74..1659f051 100644
--- a/tests/handling/test_delays.py
+++ b/tests/handling/test_delays.py
@@ -1,8 +1,8 @@
 import asyncio
-import datetime
 import logging
 
 import freezegun
+import iso8601
 import pytest
 
 import kopf
@@ -18,7 +18,7 @@
 
 @pytest.mark.parametrize('cause_reason', HANDLER_REASONS)
 @pytest.mark.parametrize('now, delayed_iso, delay', [
-    ['2020-01-01T00:00:00', '2020-01-01T00:04:56.789000', 4 * 60 + 56.789],
+    ['2020-01-01T00:00:00', '2020-01-01T00:04:56.789000+00:00', 4 * 60 + 56.789],
 ], ids=['fast'])
 async def test_delayed_handlers_progress(
         registry, settings, handlers, resource, cause_mock, cause_reason,
@@ -66,8 +66,8 @@ async def test_delayed_handlers_progress(
 
 @pytest.mark.parametrize('cause_reason', HANDLER_REASONS)
 @pytest.mark.parametrize('now, delayed_iso, delay', [
-    ['2020-01-01T00:00:00', '2020-01-01T00:04:56.789000', 4 * 60 + 56.789],
-    ['2020-01-01T00:00:00', '2099-12-31T23:59:59.000000', WAITING_KEEPALIVE_INTERVAL],
+    ['2020-01-01T00:00:00', '2020-01-01T00:04:56.789000+00:00', 4 * 60 + 56.789],
+    ['2020-01-01T00:00:00', '2099-12-31T23:59:59.000000+00:00', WAITING_KEEPALIVE_INTERVAL],
 ], ids=['fast', 'slow'])
 async def test_delayed_handlers_sleep(
         registry, settings, handlers, resource, cause_mock, cause_reason,
@@ -76,8 +76,8 @@ async def test_delayed_handlers_sleep(
 
     # Simulate the original persisted state of the resource.
     # Make sure the finalizer is added since there are mandatory deletion handlers.
-    started_dt = datetime.datetime.fromisoformat('2000-01-01T00:00:00')  # long time ago is fine.
-    delayed_dt = datetime.datetime.fromisoformat(delayed_iso)
+    started_dt = iso8601.parse_date('2000-01-01T00:00:00')  # long time ago is fine.
+    delayed_dt = iso8601.parse_date(delayed_iso)
     event_type = None if cause_reason == Reason.RESUME else 'irrelevant'
     event_body = {
         'metadata': {'finalizers': [settings.persistence.finalizer]},
diff --git a/tests/handling/test_timing_consistency.py b/tests/handling/test_timing_consistency.py
index 97e485d1..81d001ab 100644
--- a/tests/handling/test_timing_consistency.py
+++ b/tests/handling/test_timing_consistency.py
@@ -2,6 +2,7 @@
 import datetime
 
 import freezegun
+import iso8601
 
 import kopf
 from kopf._cogs.structs.ephemera import Memo
@@ -34,7 +35,7 @@ async def test_consistent_awakening(registry, settings, resource, k8s_mocked, mo
     """
 
     # Simulate that the object is scheduled to be awakened between the watch-event and sleep.
-    ts0 = datetime.datetime(2019, 12, 30, 10, 56, 43)
+    ts0 = iso8601.parse_date('2019-12-30T10:56:43')
     tsA_triggered = "2019-12-30T10:56:42.999999"
     ts0_scheduled = "2019-12-30T10:56:43.000000"
     tsB_delivered = "2019-12-30T10:56:43.000001"
@@ -56,7 +57,7 @@ def move_to_tsB(*_, **__):
     # Simulate the call as if the event has just arrived on the watch-stream.
     # Another way (the same effect): process_changing_cause() and its result.
     with freezegun.freeze_time(tsA_triggered) as frozen_dt:
-        assert datetime.datetime.utcnow() < ts0  # extra precaution
+        assert datetime.datetime.now(datetime.timezone.utc) < ts0  # extra precaution
         await process_resource_event(
             lifecycle=kopf.lifecycles.all_at_once,
             registry=registry,
@@ -68,7 +69,7 @@ def move_to_tsB(*_, **__):
             raw_event={'type': 'ADDED', 'object': body},
             event_queue=asyncio.Queue(),
         )
-        assert datetime.datetime.utcnow() > ts0  # extra precaution
+        assert datetime.datetime.now(datetime.timezone.utc) > ts0  # extra precaution
 
     assert state_store.called
 
diff --git a/tests/peering/test_peer_patching.py b/tests/peering/test_peer_patching.py
index f7c2803f..64cc025e 100644
--- a/tests/peering/test_peer_patching.py
+++ b/tests/peering/test_peer_patching.py
@@ -46,7 +46,7 @@ async def test_touching_a_peer_stores_it(
     patch = await patch_mock.call_args_list[0][0][0].json()
     assert set(patch['status']) == {'id1'}
     assert patch['status']['id1']['priority'] == 0
-    assert patch['status']['id1']['lastseen'] == '2020-12-31T23:59:59.123456'
+    assert patch['status']['id1']['lastseen'] == '2020-12-31T23:59:59.123456+00:00'
     assert patch['status']['id1']['lifetime'] == 60
 
 
diff --git a/tests/peering/test_peers.py b/tests/peering/test_peers.py
index b677a55c..a0291d48 100644
--- a/tests/peering/test_peers.py
+++ b/tests/peering/test_peers.py
@@ -1,6 +1,7 @@
 import datetime
 
 import freezegun
+import iso8601
 
 from kopf._core.engines.peering import Peer
 
@@ -10,14 +11,14 @@ def test_defaults():
     peer = Peer(identity='id')
     assert peer.identity == 'id'
     assert peer.lifetime == datetime.timedelta(seconds=60)
-    assert peer.lastseen == datetime.datetime(2020, 12, 31, 23, 59, 59, 123456)
+    assert peer.lastseen == iso8601.parse_date('2020-12-31T23:59:59.123456')
 
 
 @freezegun.freeze_time('2020-12-31T23:59:59.123456')
 def test_repr():
     peer = Peer(identity='some-id')
     text = repr(peer)
-    assert text == "<Peer some-id: priority=0, lifetime=60, lastseen='2020-12-31T23:59:59.123456'>"
+    assert text == "<Peer some-id: priority=0, lifetime=60, lastseen='2020-12-31T23:59:59.123456+00:00'>"
 
 
 @freezegun.freeze_time('2020-12-31T23:59:59.123456')
@@ -47,13 +48,13 @@ def test_creation_with_lifetime_unspecified():
 @freezegun.freeze_time('2020-12-31T23:59:59.123456')
 def test_creation_with_lastseen_as_string():
     peer = Peer(identity='id', lastseen='2020-01-01T12:34:56.789123')
-    assert peer.lastseen == datetime.datetime(2020, 1, 1, 12, 34, 56, 789123)
+    assert peer.lastseen == iso8601.parse_date('2020-01-01T12:34:56.789123')
 
 
 @freezegun.freeze_time('2020-12-31T23:59:59.123456')
 def test_creation_with_lastseen_unspecified():
     peer = Peer(identity='id')
-    assert peer.lastseen == datetime.datetime(2020, 12, 31, 23, 59, 59, 123456)
+    assert peer.lastseen == iso8601.parse_date('2020-12-31T23:59:59.123456')
 
 
 @freezegun.freeze_time('2020-12-31T23:59:59.123456')
@@ -64,8 +65,8 @@ def test_creation_as_alive():
         lastseen='2020-12-31T23:59:50.123456',  # less than 10 seconds before "now"
     )
     assert peer.lifetime == datetime.timedelta(seconds=10)
-    assert peer.lastseen == datetime.datetime(2020, 12, 31, 23, 59, 50, 123456)
-    assert peer.deadline == datetime.datetime(2021, 1, 1, 0, 0, 0, 123456)
+    assert peer.lastseen == iso8601.parse_date('2020-12-31T23:59:50.123456')
+    assert peer.deadline == iso8601.parse_date('2021-01-01T00:00:00.123456')
     assert peer.is_dead is False
 
 
@@ -77,6 +78,6 @@ def test_creation_as_dead():
         lastseen='2020-12-31T23:59:49.123456',  # 10 seconds before "now" sharp
     )
     assert peer.lifetime == datetime.timedelta(seconds=10)
-    assert peer.lastseen == datetime.datetime(2020, 12, 31, 23, 59, 49, 123456)
-    assert peer.deadline == datetime.datetime(2020, 12, 31, 23, 59, 59, 123456)
+    assert peer.lastseen == iso8601.parse_date('2020-12-31T23:59:49.123456')
+    assert peer.deadline == iso8601.parse_date('2020-12-31T23:59:59.123456')
     assert peer.is_dead is True
diff --git a/tests/persistence/test_states.py b/tests/persistence/test_states.py
index 32714230..d0b0b1b1 100644
--- a/tests/persistence/test_states.py
+++ b/tests/persistence/test_states.py
@@ -2,6 +2,7 @@
 from unittest.mock import Mock
 
 import freezegun
+import iso8601
 import pytest
 
 from kopf._cogs.configs.progress import SmartProgressStorage, StatusProgressStorage
@@ -12,14 +13,14 @@
 from kopf._core.intents.causes import HANDLER_REASONS, Reason
 
 # Timestamps: time zero (0), before (B), after (A), and time zero+1s (1).
-TSB = datetime.datetime(2020, 12, 31, 23, 59, 59)
-TS0 = datetime.datetime(2020, 12, 31, 23, 59, 59, 123456)
-TS1 = datetime.datetime(2021,  1,  1, 00, 00, 00, 123456)
-TSA = datetime.datetime(2020, 12, 31, 23, 59, 59, 999999)
-TSB_ISO = '2020-12-31T23:59:59.000000'
-TS0_ISO = '2020-12-31T23:59:59.123456'
-TS1_ISO = '2021-01-01T00:00:00.123456'
-TSA_ISO = '2020-12-31T23:59:59.999999'
+TSB_ISO = '2020-12-31T23:59:59.000000+00:00'
+TS0_ISO = '2020-12-31T23:59:59.123456+00:00'
+TS1_ISO = '2021-01-01T00:00:00.123456+00:00'
+TSA_ISO = '2020-12-31T23:59:59.999999+00:00'
+TSB = iso8601.parse_date(TSB_ISO)
+TS0 = iso8601.parse_date(TS0_ISO)
+TS1 = iso8601.parse_date(TS1_ISO)
+TSA = iso8601.parse_date(TSA_ISO)
 ZERO_DELTA = datetime.timedelta(seconds=0)