diff --git a/app/build.gradle b/app/build.gradle
index ee3bb251..237ebe43 100644
--- a/app/build.gradle
+++ b/app/build.gradle
@@ -250,6 +250,10 @@ dependencies {
     implementation "com.github.lisawray.groupie:groupie:$groupie_version"
     implementation "com.github.lisawray.groupie:groupie-viewbinding:$groupie_version"
 
+    // Kronos ntp clock
+    def kronos_latest_version = "0.0.1-alpha09"
+    implementation "com.lyft.kronos:kronos-android:$kronos_latest_version"
+
     //// TEST RELATED DEPENDENCIES
     testImplementation "org.jetbrains.kotlin:kotlin-test-junit5:$kotlin_version"
 
diff --git a/app/src/main/java/org/covidwatch/android/BaseCovidWatchApplication.kt b/app/src/main/java/org/covidwatch/android/BaseCovidWatchApplication.kt
index f7b01472..33a49aec 100644
--- a/app/src/main/java/org/covidwatch/android/BaseCovidWatchApplication.kt
+++ b/app/src/main/java/org/covidwatch/android/BaseCovidWatchApplication.kt
@@ -2,6 +2,7 @@ package org.covidwatch.android
 
 import android.app.Application
 import kotlinx.coroutines.GlobalScope
+import org.covidwatch.android.data.NtpTime
 import org.covidwatch.android.di.appModule
 import org.covidwatch.android.di.flavorSpecificModule
 import org.covidwatch.android.domain.ProvideDiagnosisKeysUseCase
@@ -18,6 +19,7 @@ open class BaseCovidWatchApplication : Application() {
     private val updateRegionsUseCase: UpdateRegionsUseCase by inject()
     private val removeOldExposuresUseCase: RemoveOldDataUseCase by inject()
     private val provideDiagnosisKeysUseCase: ProvideDiagnosisKeysUseCase by inject()
+    private val ntpTime: NtpTime by inject()
 
     override fun onCreate() {
         super.onCreate()
@@ -36,5 +38,7 @@ open class BaseCovidWatchApplication : Application() {
             launchUseCase(removeOldExposuresUseCase)
             launchUseCase(updateRegionsUseCase)
         }
+
+        ntpTime.syncInBackground()
     }
 }
diff --git a/app/src/main/java/org/covidwatch/android/data/NtpTime.kt b/app/src/main/java/org/covidwatch/android/data/NtpTime.kt
new file mode 100644
index 00000000..e05c72e9
--- /dev/null
+++ b/app/src/main/java/org/covidwatch/android/data/NtpTime.kt
@@ -0,0 +1,19 @@
+package org.covidwatch.android.data
+
+import android.content.Context
+import com.lyft.kronos.AndroidClockFactory
+import com.lyft.kronos.KronosClock
+import java.time.Instant
+import java.time.LocalDate
+import java.time.LocalDateTime
+import java.time.ZoneId
+
+class NtpTime (context : Context) {
+    private val kronosClock : KronosClock = AndroidClockFactory.createKronosClock(context)
+
+    fun currentTimeMillis() : Long = kronosClock.getCurrentTimeMs()
+
+    fun syncInBackground() = kronosClock.syncInBackground()
+
+    fun nowAsInstant() : Instant = Instant.ofEpochMilli(currentTimeMillis())
+}
diff --git a/app/src/main/java/org/covidwatch/android/di/AppModule.kt b/app/src/main/java/org/covidwatch/android/di/AppModule.kt
index 7ba96ab5..09b8f9ea 100644
--- a/app/src/main/java/org/covidwatch/android/di/AppModule.kt
+++ b/app/src/main/java/org/covidwatch/android/di/AppModule.kt
@@ -181,6 +181,10 @@ val appModule = module {
         )
     }
 
+    single {
+        NtpTime(androidApplication())
+    }
+
     factory {
         ProvideDiagnosisKeysUseCase(
             workManager = get(),
diff --git a/app/src/main/java/org/covidwatch/android/extension/Instant.kt b/app/src/main/java/org/covidwatch/android/extension/Instant.kt
new file mode 100644
index 00000000..e152a1d2
--- /dev/null
+++ b/app/src/main/java/org/covidwatch/android/extension/Instant.kt
@@ -0,0 +1,8 @@
+package org.covidwatch.android.extension
+
+import java.time.Instant
+import java.time.temporal.ChronoUnit
+
+fun Instant.plusDays(daysToAdd : Long) : Instant = plus(daysToAdd, ChronoUnit.DAYS)
+
+fun Instant.minusDays(daysToSubtract : Long) : Instant = minus(daysToSubtract, ChronoUnit.DAYS)
diff --git a/app/src/main/java/org/covidwatch/android/ui/reporting/VerifyPositiveDiagnosisFragment.kt b/app/src/main/java/org/covidwatch/android/ui/reporting/VerifyPositiveDiagnosisFragment.kt
index 038e05d3..279d2658 100644
--- a/app/src/main/java/org/covidwatch/android/ui/reporting/VerifyPositiveDiagnosisFragment.kt
+++ b/app/src/main/java/org/covidwatch/android/ui/reporting/VerifyPositiveDiagnosisFragment.kt
@@ -14,19 +14,21 @@ import com.google.android.material.datepicker.CalendarConstraints
 import com.google.android.material.datepicker.MaterialDatePicker
 import com.google.android.material.textfield.TextInputLayout
 import org.covidwatch.android.R
+import org.covidwatch.android.data.NtpTime
 import org.covidwatch.android.databinding.FragmentVerifyPositiveDiagnosisBinding
+import org.covidwatch.android.extension.minusDays
 import org.covidwatch.android.extension.observe
 import org.covidwatch.android.extension.observeEvent
 import org.covidwatch.android.extension.observeNullableEvent
-import org.covidwatch.android.extension.toInstant
 import org.covidwatch.android.ui.BaseViewModelFragment
+import org.koin.android.ext.android.inject
 import org.koin.androidx.viewmodel.ext.android.stateViewModel
-import java.time.LocalDate
 
 class VerifyPositiveDiagnosisFragment :
     BaseViewModelFragment<FragmentVerifyPositiveDiagnosisBinding, VerifyPositiveDiagnosisViewModel>() {
 
     override val viewModel: VerifyPositiveDiagnosisViewModel by stateViewModel()
+    private val ntpTime: NtpTime by inject()
 
     override fun bind(
         inflater: LayoutInflater,
@@ -119,15 +121,16 @@ class VerifyPositiveDiagnosisFragment :
         val builder = MaterialDatePicker.Builder.datePicker()
         val constraints = CalendarConstraints.Builder()
 
-        val twoWeeksAgo = LocalDate.now().plusDays(-14).toInstant()
-            .toEpochMilli()
+        val twoWeeksAgo = ntpTime.nowAsInstant().minusDays(14).toEpochMilli()
 
         // Day in the past or 14 days back
         val fromWhen = dayInPast ?: twoWeeksAgo
 
-        val untilNow = LocalDate.now().toInstant().toEpochMilli()
+        val untilNow = ntpTime.currentTimeMillis()
 
-        constraints.setValidator(BaseDateValidator { it in fromWhen..untilNow })
+        constraints
+            .setValidator(BaseDateValidator { it in fromWhen..untilNow })
+            .setOpenAt(untilNow)
 
         val datePicker = builder
             .setSelection(selection)