I revised 2 months before my exams, as I always have done, for a few hours each day, and my average was 97.5% UMS at AS. Of course it can be done with two months revision. That's far earlier than when the average student starts, and provided that you have average intelligence, you should do really well with about 2 month's of proper, robust and effective revision- and by that, I mean writing out the text book/sections of it as many times as you can. Don't just read it and expect to retain all of the information.
Also sod the mocks, mine are this week and I haven't revised for them at all. As I said, it takes 2 months of revision for me to be at optimum levels of preparedness for exams, and if my teachers ever thought I was going to be revising from December, then they misunderstand the teenage psyche.