It depends, I am in the same boat as you I have just done my GCSES and I am going onto alevels, and ill just say that I will be doing alot! I am aiming for 4A's .. so thats a lot of work. Each night I will be doing quite a bit of revision and reading ahead!
I started during the Easter holidays for AS and I roughly did 5-6 hours of revision per non-school day either doing past papers, making notes or watching video's online to understand concepts. I'd say I spent about 80% of my revision time doing past papers and my hours started bumping up to 6-7 during exam period.
For reference I take maths,further maths, biology and chemistry and got AAAB with the B in biology, getting it remarked though since I was certain I got a high A after coming out the exam. This will differ from person to person, my friend got 4 A's and he did half the amount of time I did so you'll just have to find the amount of hours which works best for you and allows you to be the most productive. Going above 7 hours for me just made me exhausted while my other friend could do 8 hours and feel fine. Hope this gave you some insight
I didn't do too much and only really started about 2 weeks before the exams going through the past papers and I got 4A*'s. So I guess it depends on the person really. Would you feel comfortable walking in to your exam knowing you'd done as little as me?