Hi Kelly! Truthfully, it depends on your study styles/ habits as well as your background knowledge. Personally, I bought the ACSM Resources book and read it word for word, taking notes, and not skipping anything. Then, I bought one of the older versions of the certification review (I did not find the new one to be as good) and did all of the chapter questions and quizzes. In all, it took me about 3 months from beginning to end.
Hope this helps,