diff --git a/Normal/Services/TimedUnblockService.swift b/Normal/Services/TimedUnblockService.swift
index 9a01598..aee7035 100644
--- a/Normal/Services/TimedUnblockService.swift
+++ b/Normal/Services/TimedUnblockService.swift
@@ -64,7 +64,7 @@ final class TimedUnblockService {
         cancelMonitoring(activityName: activityName)
 
         let start = clock()
-        let endDate = start.addingTimeInterval(duration.timeInterval)
+        let endDate = Self.endDate(of: duration, from: start)
         try scheduleActivity(name: activityName, start: start, endDate: endDate)
 
         try persist(
@@ -95,7 +95,7 @@ final class TimedUnblockService {
         cancelMonitoring(activityName: activityName)
 
         let start = clock()
-        let endDate = start.addingTimeInterval(duration.timeInterval)
+        let endDate = Self.endDate(of: duration, from: start)
         try scheduleActivity(name: activityName, start: start, endDate: endDate)
 
         try persist(
@@ -280,6 +280,11 @@ final class TimedUnblockService {
         }
     }
 
+    private static func endDate(of duration: TimedUnblockDuration, from start: Date) -> Date {
+        let end = start.addingTimeInterval(duration.timeInterval).timeIntervalSinceReferenceDate
+        return Date(timeIntervalSinceReferenceDate: end.rounded(.down))
+    }
+
     private func scheduleActivity(name: String, start: Date, endDate: Date) throws {
         let schedule = DeviceActivityScheduleFactory.window(from: start, to: endDate)
         try activityCenter.startMonitoring(
diff --git a/NormalTests/Services/BlockingScenarioTests.swift b/NormalTests/Services/BlockingScenarioTests.swift
index 0f4b150..d101766 100644
--- a/NormalTests/Services/BlockingScenarioTests.swift
+++ b/NormalTests/Services/BlockingScenarioTests.swift
@@ -275,6 +275,27 @@ struct BlockingScenarioTests {
         #expect(h.blocked == h.apps(1, 2))
     }
 
+    @Test func timedUnblockAllStartedMidSecondReblocksAtItsRegisteredEnd() throws {
+        let h = BlockingHarness()
+        h.blockAll()
+        h.passTime(to: h.at(10).addingTimeInterval(0.6))
+        try h.unblockAllTimed(.thirtyMinutes)
+
+        h.wake(at: try h.registeredEnd(of: SharedConstants.mainTimedUnblockActivityName))
+        #expect(h.blocked == h.apps(1, 2, 3))
+    }
+
+    @Test func groupTimedUnblockStartedMidSecondReblocksAtItsRegisteredEnd() throws {
+        let h = BlockingHarness()
+        h.blockAll()
+        let social = h.group([1, 2])
+        h.passTime(to: h.at(10).addingTimeInterval(0.6))
+        try h.unblockGroupTimed(social, .oneHour)
+
+        h.wake(at: try h.registeredEnd(of: SharedConstants.groupTimedUnblockActivityName(for: social.id)))
+        #expect(h.blocked == h.apps(1, 2, 3))
+    }
+
     @Test func blockingAGroupDuringTimedUnblockAllAppliesNowAndAfter() throws {
         let h = BlockingHarness()
         h.blockAll()
diff --git a/NormalTests/Services/TimedUnblockServiceTests.swift b/NormalTests/Services/TimedUnblockServiceTests.swift
index 98f168c..2c47805 100644
--- a/NormalTests/Services/TimedUnblockServiceTests.swift
+++ b/NormalTests/Services/TimedUnblockServiceTests.swift
@@ -123,7 +123,8 @@ struct TimedUnblockServiceTests {
         let dto = try #require(store.timedUnblocks.first)
         let start = try #require(dto.startDate)
         #expect(start >= before)
-        #expect(dto.endDate.timeIntervalSince(start) == 5700)
+        let length = dto.endDate.timeIntervalSince(start)
+        #expect(length > 5699 && length <= 5700)
         #expect(service.activeUnblockStartDates()[TimedUnblockService.mainID] == start)
     }
 
diff --git a/NormalTests/TestSupport/BlockingHarness.swift b/NormalTests/TestSupport/BlockingHarness.swift
index 6e81097..8880fae 100644
--- a/NormalTests/TestSupport/BlockingHarness.swift
+++ b/NormalTests/TestSupport/BlockingHarness.swift
@@ -1,7 +1,9 @@
+import DeviceActivity
 import FamilyControls
 import Foundation
 import ManagedSettings
 @testable import Normal
+import Testing
 
 @MainActor
 final class BlockingHarness {
@@ -81,6 +83,11 @@ final class BlockingHarness {
         Set(ids.map(TokenFixtures.app))
     }
 
+    func registeredEnd(of activityName: String) throws -> Date {
+        let schedule = try #require(activity.registeredSchedule(for: DeviceActivityName(activityName)))
+        return try #require(Calendar.current.date(from: schedule.intervalEnd))
+    }
+
     func passTime(to date: Date) {
         clock.now = date
     }