WolfLarson:
Unfortunately, each of us will need to answer that question for our self. There will be individual who can take this exam cold and still do fairly well. For example there is W6BF on page 9 of the 509+ thread:
1) 511 total 127 PC | 130 CARS | 128 Bio | 126 Psy/Soc
2) Never studied
3) Never looked at any materials
4) Never took a practice test
5) Majored in Bio + Latin, Minored in Chem
6) I would recommend studying, even though I did not study
7) Never
I meant to study, but I was really busy - and I figured I would just see how I did. I got a competitive-ish score, and went with it. I only got into one med school.
My suggestion is take a practice test and see where you are currently. That will tell you just how much work you need to put in. You will need to do as much practice as you see necessary to get to the score that you will be happy with. All AAMC practice material should be the minimum. That does not mean you should ignore content review--content is also important. So the question becomes, how quickly can you relearn/re-familiarize yourself with the necessary content and then do a ton of practice (or at least all AAMC)?
Realize that the people doing USMLE just finish taking a test or three every week on the subject matter for the past year or so... Basically the content is still relatively fresh.
There will be some who only need a month or two to study, others may need a full nine months, while an average it will be three to four months for most? How fresh is your content? How strong is your content knowledge? How strong is your reasoning skills? How well did you do on the Verbal Reasoning section when you took it both times in the pass?
I believe with your previous scores you are going to need a minimum of 3-4 months. You do need content review and plenty of time to take a ton of practice problems. The among of work that you put in those practice problems (reviewing) will determine whether you improve or get the equivalent of your past scores. Best of luck on your journey my friend.
Oh, don't forget that you also need to study for Psychology and Sociology for this current exam.