I think 2-3 months is good, depending on how much you need to review vs. relearn. I used the Kaplan big blue book which I bought on Amazon for about $20. I also watched Khan Academy, but I would save that for topics that you aren't understanding because it would take forever to watch them all.
I set a schedule that would cover 1-2 chapters from the Kaplan book per day, and I took busy days off. I supplemented my reading with related videos from Khan Academy. I tried to leave a few weeks before the test to just take practice tests and review. I got a little behind, and a few sections were lower than I would have liked, but overall I did very well, so I think it was fairly successful.