Very hard to say how much time is required for each exam. I sat FAR/AA/TC all in one sitting and it did take a fair amount of revision. Usually a couple hours every weekday after college/work and 10 hours across the weekend on average. Everyone's different though, and you can't really wing any of the professional/advanced stage exams.
I wouldn't bother going over the content before you start, that's probably a waste of time. Best to go over things you've missed/unsure about in class that same evening. As I sat 3 at a time, I split my time roughly 40-40-20 across FAR-TC-AA. You don't need as much time for AA - the syllabus is smaller than the other two and it's generally easier in my opinion.