WorkingHours only has limited control over how iOS refreshes the widget. It can request a widget refresh, but iOS does not guarantee that the widget redraws immediately.
Does the Live Activity update immediately? Do the normal WorkingHours notifications show when starting/stopping the timer via the widget? Does the timer start/stop correctly inside the app when you control it via the widget?
Do you have Cloud Sync enabled? If yes, which sync provider are you using? As a quick test, does the delay still happen if Cloud Sync is temporarily disabled?
Did you already try restarting iOS to see if that helps?
Also, is there a specific reason why you are still on iOS 26.3? This may not be related, but if a newer iOS version is available on your device, please try updating and check whether the widget behavior changes.