diff --git a/mobile/ios-app/App/HermesRepository.swift b/mobile/ios-app/App/HermesRepository.swift
index 5fbe45a..d657dcf 100644
--- a/mobile/ios-app/App/HermesRepository.swift
+++ b/mobile/ios-app/App/HermesRepository.swift
@@ -1,3 +1,4 @@
+import AVFoundation
 import Combine
 import Foundation
 
@@ -239,9 +240,12 @@ enum MockHermesData {
         winningOutcomeID: String,
         now: Date
     ) -> HermesRound {
-        let lockAt = now.addingTimeInterval(15)
-        let settleAt = lockAt.addingTimeInterval(6)
         let mediaURL = localMediaURL(named: "example-round.mov") ?? fallbackMediaURL
+        let previewDurationMs = assetDurationMs(url: mediaURL) ?? 15_000
+        let revealURL = revealMediaURL()
+        let revealDurationMs = assetDurationMs(url: revealURL) ?? 6_000
+        let lockAt = now.addingTimeInterval(Double(previewDurationMs) / 1_000.0)
+        let settleAt = lockAt.addingTimeInterval(6)
 
         let event = HermesEvent(
             id: UUID(uuidString: eventID) ?? UUID(),
@@ -251,9 +255,9 @@ enum MockHermesData {
             titleSv: promptKey,
             status: "active",
             previewStartMs: 0,
-            previewEndMs: 12_000,
-            revealStartMs: 12_000,
-            revealEndMs: 18_000,
+            previewEndMs: previewDurationMs,
+            revealStartMs: 0,
+            revealEndMs: revealDurationMs,
             lockAt: lockAt,
             settleAt: settleAt
         )
@@ -264,11 +268,11 @@ enum MockHermesData {
             mediaType: "hls_main",
             hlsMasterUrl: mediaURL,
             posterUrl: nil,
-            durationMs: 18_000,
+            durationMs: previewDurationMs,
             previewStartMs: 0,
-            previewEndMs: 12_000,
-            revealStartMs: 12_000,
-            revealEndMs: 18_000
+            previewEndMs: previewDurationMs,
+            revealStartMs: 0,
+            revealEndMs: revealDurationMs
         )
 
         let marketUUID = UUID(uuidString: marketID) ?? UUID()
@@ -336,4 +340,13 @@ enum MockHermesData {
         let candidate = repoRoot.appendingPathComponent(fileName)
         return FileManager.default.fileExists(atPath: candidate.path) ? candidate : nil
     }
+
+    private static func assetDurationMs(url: URL) -> Int? {
+        let duration = AVAsset(url: url).duration.seconds
+        guard duration.isFinite, duration > 0 else {
+            return nil
+        }
+
+        return Int((duration * 1_000.0).rounded())
+    }
 }
diff --git a/mobile/ios-app/Features/Round/RoundView.swift b/mobile/ios-app/Features/Round/RoundView.swift
index 08a85da..716bb66 100644
--- a/mobile/ios-app/Features/Round/RoundView.swift
+++ b/mobile/ios-app/Features/Round/RoundView.swift
@@ -38,7 +38,8 @@ struct RoundView: View {
         TimelineView(.periodic(from: Date(), by: 1)) { _ in
             let round = repository.currentRound
             let now = repository.serverNow()
-            let remaining = max(lockAt.timeIntervalSince(now), 0)
+            let activeLockAt = round?.event.lockAt ?? lockAt
+            let remaining = max(activeLockAt.timeIntervalSince(now), 0)
             let timerLocked = round != nil && remaining <= 0
             let bannerMessage = actionMessage ?? hermesUserFacingErrorMessage(
                 localization: localization,
@@ -118,7 +119,7 @@ struct RoundView: View {
 
             Spacer(minLength: 12)
 
-            SemiCircleCountdownView(progress: progressValue(for: remaining), label: Self.countdownText(for: remaining))
+            SemiCircleCountdownView(progress: progressValue(for: remaining, round: round), label: Self.countdownText(for: remaining))
         }
         .padding(.horizontal, HermesTheme.screenPadding)
         .padding(.top, 112)
@@ -382,7 +383,7 @@ struct RoundView: View {
                     }
 
                     phase = .reveal
-                    playerCoordinator.play(url: revealMediaURL(for: round), startTimeMs: round.media.revealStartMs, rate: 1.0)
+                    playerCoordinator.play(url: revealMediaURL(for: round), startTimeMs: revealStartTimeMs(for: round), rate: 1.0)
                     analytics.track("reveal_started", attributes: roundAnalyticsAttributes(round).merging(baseSelectionAttributes(selectedOutcomeID)) { _, new in new })
                 }
             } catch {
@@ -430,6 +431,10 @@ struct RoundView: View {
         repository.currentSession?.deviceModel == "Demo Device" ? MockHermesData.revealMediaURL() : round.media.hlsMasterUrl
     }
 
+    private func revealStartTimeMs(for round: HermesRound) -> Int {
+        repository.currentSession?.deviceModel == "Demo Device" ? 0 : round.media.revealStartMs
+    }
+
     private func promptTitle(for round: HermesRound?) -> String {
         guard let round else {
             return localization.string(for: "common.loading")
@@ -488,8 +493,9 @@ struct RoundView: View {
         return outcomeTitle(outcome)
     }
 
-    private func progressValue(for remaining: TimeInterval) -> Double {
-        min(max(remaining / 15.0, 0), 1)
+    private func progressValue(for remaining: TimeInterval, round: HermesRound?) -> Double {
+        let totalDuration = round.map { Double(max($0.media.previewEndMs - $0.media.previewStartMs, 1)) / 1_000.0 } ?? 15.0
+        return min(max(remaining / totalDuration, 0), 1)
     }
 
     private static func countdownText(for remaining: TimeInterval) -> String {