3 weeks before UCAT's, how long should I aim to revise?Watch this thread
Secondly, when are you taking the UCAT? Two hours a day is a lot, especially if your exam isn't for a month or more. The UCAT consortium recommend about 25-35 hours over 4-6 weeks, which to me sounds about right. I would say there's no right amount of revision - you need to get to a point where you're comfortable and confident with the format and the timings, and not burn out. Ideally, have a timetable, and revise intelligently rather than focusing on how long you've revised for - note down your scores, focus on your worst sections, identify the mistakes you make and work actively to correct them. Ultimately, you've revised for exams before, and you know what works for you.
edit: I've just read the title which is "3 weeks until UCAT", lol. The rest of the advice still holds, but two hours a day probably makes more sense if you're on that kind of accelerated schedule But rest and not burning out is still important! Taking the odd day off often does more good than anything else.