I would create a timetable on excel and really just try not to put too many hours of constant revision in. You won't learn much believe me. I'd try and stick to an hour at a time and then have a 10/15 minute break to get yourself ready for the next hour. There is no correct amount of hours you should be revising because its all down to personal preference. You could revise less than everyone else but still come out with great grades. It's all down to how effective your revision strategies are. Try to take it easy for now and then maybe think about doing a little more.