diff --git a/monitoring/monitorlib/mutate/rid.py b/monitoring/monitorlib/mutate/rid.py
index 1661fd41ee..09fbe25cf0 100644
--- a/monitoring/monitorlib/mutate/rid.py
+++ b/monitoring/monitorlib/mutate/rid.py
@@ -97,8 +97,8 @@ def upsert_subscription(
     area_vertices: List[s2sphere.LatLng],
     alt_lo: float,
     alt_hi: float,
-    start_time: datetime.datetime,
-    end_time: datetime.datetime,
+    start_time: Optional[datetime.datetime],
+    end_time: Optional[datetime.datetime],
     uss_base_url: str,
     subscription_id: str,
     rid_version: RIDVersion,
diff --git a/monitoring/monitorlib/rid_v1.py b/monitoring/monitorlib/rid_v1.py
index 60780ce1d9..08a51ce168 100644
--- a/monitoring/monitorlib/rid_v1.py
+++ b/monitoring/monitorlib/rid_v1.py
@@ -23,8 +23,8 @@ def make_volume_4d(
     vertices: List[s2sphere.LatLng],
     alt_lo: float,
     alt_hi: float,
-    start_time: datetime.datetime,
-    end_time: datetime.datetime,
+    start_time: Optional[datetime.datetime],
+    end_time: Optional[datetime.datetime],
 ) -> Volume4D:
     return ImplicitDict.parse(
         {
@@ -38,8 +38,16 @@ def make_volume_4d(
                 "altitude_lo": alt_lo,
                 "altitude_hi": alt_hi,
             },
-            "time_start": StringBasedDateTime(start_time),
-            "time_end": StringBasedDateTime(end_time),
+            **(
+                {"time_start": StringBasedDateTime(start_time)}
+                if start_time is not None
+                else {}
+            ),
+            **(
+                {"time_end": StringBasedDateTime(end_time)}
+                if end_time is not None
+                else {}
+            ),
         },
         Volume4D,
     )
diff --git a/monitoring/monitorlib/rid_v2.py b/monitoring/monitorlib/rid_v2.py
index fbad7f5947..0183f03755 100644
--- a/monitoring/monitorlib/rid_v2.py
+++ b/monitoring/monitorlib/rid_v2.py
@@ -1,5 +1,5 @@
 import datetime
-from typing import List
+from typing import List, Optional
 
 import s2sphere
 from implicitdict import ImplicitDict, StringBasedDateTime
@@ -33,8 +33,8 @@ def make_volume_4d(
     vertices: List[s2sphere.LatLng],
     alt_lo: float,
     alt_hi: float,
-    start_time: datetime.datetime,
-    end_time: datetime.datetime,
+    start_time: Optional[datetime.datetime],
+    end_time: Optional[datetime.datetime],
 ) -> Volume4D:
     return ImplicitDict.parse(
         {
@@ -48,8 +48,16 @@ def make_volume_4d(
                 "altitude_lower": make_altitude(alt_lo),
                 "altitude_upper": make_altitude(alt_hi),
             },
-            "time_start": make_time(start_time),
-            "time_end": make_time(end_time),
+            **(
+                {"time_start": StringBasedDateTime(start_time)}
+                if start_time is not None
+                else {}
+            ),
+            **(
+                {"time_end": StringBasedDateTime(end_time)}
+                if end_time is not None
+                else {}
+            ),
         },
         Volume4D,
     )
diff --git a/monitoring/uss_qualifier/scenarios/astm/netrid/dss_wrapper.py b/monitoring/uss_qualifier/scenarios/astm/netrid/dss_wrapper.py
index d18ef2b063..d5e14263ca 100644
--- a/monitoring/uss_qualifier/scenarios/astm/netrid/dss_wrapper.py
+++ b/monitoring/uss_qualifier/scenarios/astm/netrid/dss_wrapper.py
@@ -775,8 +775,8 @@ def put_sub_expect_response_code(
         area_vertices: List[s2sphere.LatLng],
         alt_lo: float,
         alt_hi: float,
-        start_time: datetime.datetime,
-        end_time: datetime.datetime,
+        start_time: Optional[datetime.datetime],
+        end_time: Optional[datetime.datetime],
         expected_error_codes: Set[int],
         uss_base_url: str,
         sub_id: str,
@@ -823,8 +823,8 @@ def put_sub(
         area_vertices: List[s2sphere.LatLng],
         alt_lo: float,
         alt_hi: float,
-        start_time: datetime.datetime,
-        end_time: datetime.datetime,
+        start_time: Optional[datetime.datetime],
+        end_time: Optional[datetime.datetime],
         uss_base_url: str,
         sub_id: str,
         sub_version: Optional[str] = None,