If you're doing this during the holidays, don't push yourself too much, because chances are for certain things taught at School, it'll stick in your head longer.
Time Commitments are different for each and every student, and dependant again on how long your concentration span is, as well as the subjects you're doing.
Also, it might be beneficial to study subjects like Legal Studies, or English-type related (relies on alot of memorizing) in the morning to allow maximum memory absorption, and leave Maths, Chemistry, Physics (relies more on the use of formulas) till the afternoon.
Adjust your schedule accordingly, and don't try setting a timetable like "From 1pm-2pm I'll be studying Chemistry, so from 2:30-3pm I'll have a quick KFC meal"