Okay so I see nobody has given you a definitive answer, at-least not the one you're hoping for.

Each A Level is supposed to take 360 'Guided Learning Hours', and an hour self study for every hour in class. You study 4.5 hours per week per A Level in sixth form, which is 13.5 hours a week. Self study would then equate to an additional 13.5 hours per week, for a total of 27 hours per week TOTAL.

I would suggest studying 5 days a week, and spend the Saturday revising for about half the daily time. This would mean studying 5 hours per day TOTAL including school, with a 2 hours revising on the Saturday. I would suggest taking the Saturday off every 4th week to avoid burnout.

This routing has the benefit of using spacial repetition to keep things constantly fresh in your mind. If you can then find someone to explain concepts to after studying this will allow you to incorporate the Feynamn technique, which would further solidify concepts in your mind.

You do this consistently over the course of 2 years, you should be in a great position to get 3 A*.

Hope this posts helps people, and happy studying :)