I didn't start revising for 2hrs a day until March. In my opinion I think I would have burnt myself out, especially with 3! If you revise effectively its fine to start later on. Just do your homework, study for topic tests and enjoy up until Feb-March. And revise for your mocks, you'll remember more than you think when you come to revise properly. Did 5-6hrs a day during easter and about 3 during exam period. Ended up with 6A*'s, 6A's.
Best of luck and enjoy.