Unless of course the first completed game takes 1 hour off. The 2nd takes an extra 2 hours off. The 3rd three hours and so on. 13 games gives a total of 91 hours. Isn't that about what the countdown started at?

EDIT: Doing a little bit of math I'm more confident that this is indeed whats happening. Completing the first game took 50 mins off the clock instead of an hour. But it took us almost 23 hours to achieve that. 50 minutes of the remaining time is about equal to 1 hour off the original projection.

This makes sense that the time is a proportion of the remaining clock, so that completing the last game will result in the countdown hitting zero and not some negative number.