Oh, and I allmost forgot: you could just get yourself a real life stop watch, no? I mean, you'll need it anyway even if the in-game clock works or not.
The reason? because there is no in-game stop watch in the sonar room or nav-map, and those are the places where you'll need the stop watch the most. The nav map room you can get away with switching back and forth to the stopwatch, but not the sonar room. To be able to acurately determine the target's speed by the frequency of the Chug-chug noises that it makes you have to stay glued to the hydrophone station AND read precise time measurements on the stop watch at the same time :|\
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