"if this person gets promoted, they won't get more pay than otherwise when they're doing overtime a certain day" ? -- yes, because they will be a regular salar

"if this person gets promoted, they won't get more pay than otherwise when they're doing overtime a certain day" ? -- yes, because they will be a regular salaried ("exempt") employee. "by hours in a week, month?" I think there is a daily threshold, and a weekly threshold, for overtime. I don't think there is anything else. But I don't figure the pay, so I don't know the ins and outs. * Where I work, you have to justify overtime, so in effect the employee was prevented from moving work hours between days unless the resulting increase in effective wage could be justified. ("Feeling in the zone" is not enough...)