I'm doing 4 AS module resits in January along with 3 A2 modules - oh the joy.
The sooner the better obviously, you will have all your AS work completed from last year and if your unlike me your neat and tidy revision notes. I see no harm in setting aside a few hours a week now and increasing that up until January, remembering that as January approaches you're going to have to revise A2 modules.
I like to think that's good advice and i'll follow it, but in reality it's unlikely lol. Personal Statement to start and a backlog of homework.