When Mr. Freeze starts the chrono (clock) to freeze the entire town it's written 12:00, then Batman and Robin are fighting against Bane and Poison Ivy. When they beat Poison and Bane, Batman stops the chrono, (clock) it's written 11:50.
Maybe I didn't understand this right, but if the chrono clock had been set at 12:00 and was then stopped after a few minutes by Batman, then the clock would have been counting DOWN, thus ending up at the remaining time of 11:50. But i don't know, maybe someone who saw the movie could help...