In 6th grade I would literally count the minutes until history class was over and gym class started.
One day the teacher was running late and it was just us kids in the classroom. Sensing that this was my moment, I stood up, changed the time on the clock, and sat back down.
I was young, so I got greedy. I set the clock 10 minutes ahead.
It was about a week before the teacher found out. Over that week, our class got around a full extra hour of gym time.
All good things must come to an end, though.
Ms. Clark (after checking her own watch): "Hm, I think that clock is running fast"
Me: "Oh, don't worry, I'll fix it"