The contract states something like 302 hours per month before they pay overtime. They're not keen on people doing overtime at all! Everyone has to fill out a timecard of hour's worked. If you're getting near to the 302 hours, then you're supposed to let the supervisor know (if they haven't already noticed). This is so they can decide if they need to let you do overtime or not. If you don't let the supervisor know, and go over your 302 hours, you'll get into trouble (probably written warning), for unathorized overtime. Chances are, unless there's a staff shortage, the shift's will be organised by the manager's so that no-one goes over 302 hours.