When I was studying my goal was 15 hour a week, and I did that over the course of 10 weeks. I'd do 2 hours a night Monday - Thursday, take Friday night and Saturday off (I was taking the October test so Saturday's conflicted with college football) and then spend most of the day Sunday studying to make my weekly total 15 hours. I found easier to keep on track if I broke it down by a number of hours I wanted to study weekly rather then thinking about the grand total.
Of course the number of hours each person needs to study will vary from person to person it also depends on how effective your study time is. So there is no magic answer for how many hours to study to be prepared.