The 25th Hour — Keith B. Darrell

Mackenzie Mortimer is a typical junior high geek: shy, awkward, late with his homework, and always late for class. He's never got enough time to do everything he needs to do; after all, there are only 24 hours in a day. But when Mac finds his grandfather's pocket watch, he discovers his days have an extra hour. The eccentric inventor's journal reveals the watch can add up to 60 minutes to a single day by freezing time around whomever controls it. When a crisis looms for Mac and his friends, time is running out... but fortunately, Mackenzie Mortimer has a few more minutes than anyone else.