They must pay you if they required you to work overtime and pay according to company policy. Not all companies pay time and a half for overtime. The key is whether or not they asked you to work overtime.
No they have to pay you -unless you are at a salary rate or you do not work over 40 hours. If you are scheduled for 8 hours on monday and actually work 10 hours instead they are not going to cut you an overtime check until you exceed 40 hours worked. Some places will ask you to come in late or go home early on a different day to keep from paying overtime.
Most companies do not pay overtime on a daily basis. It is payed weekly on anything over 40 hrs unless you are payed salary. So it doesn't matter if you work over 8 hrs 1 day in a week if you still don't accumulate 40, you will be payed at the regular hourly rate.
It all depends on what your work rules state about overtime. Is it anything over 8 in a 24 hr cycle paid at time and a half. Or anything in excess of 40 hrs will be time and a half. Or like the one person said above. If your salary you will get your 40 hrs.