Kabaka

Could be. I have no idea how it’s implemented in this specific device/app. It might immediately resume tracking the duration when it boots (or you opened the app before correcting the time) and cancels the stopwatch when it finds the start time is seemingly in the future. If I still had my iPod Touch, I’d try to find out — decent nerd sniping opportunity.

It just has to record the start time, then show the duration between the current clock time and the saved start time. As long as the clock can still sync or be manually set after being charged, there’s no reason it shouldn’t work.