Do not treat it like GCSE, A-level is very different and at least 10 times harder. If you spend an hour doing revision for GCSE per week, you need to do at least 3 hour of revision for each subject per week. This will make you feel a lot confident and also help you in getting better grades.
Most of us won't have the patience to follow our timetable 100% tightly, so push yourself a bit harder at the beginning is ok IMO.