I spent a solid 5-6 months studying for it (October --> March). I began with light content review each week, but not everyday. Usually on weekends and weeknights where I wouldn't have too much homework. Then after Christmas break, I started concept application for a solid month alongside an AAMC practice exam every other week. Weeks up to the actual thing, just continue your content review, maybe go back and review your AAMC practice exams a bit.
But you want to know the best answer for how long you should study? Your entire undergraduate career
. Seriously, the best way to do well on the MCAT is to learn all of this material the right way the very first time you see it (undergraduate courses). Take the time to study well in your general chemistry, organic chemistry, physics, and biology courses, and make sure you are learning not just to know material for exams, but also for your own general knowledge.
"MCAT studying" is just that: studying the test. Sure, you should use this time to review content, but a lot of it should be things you've seen before. You want to use time to familiarize yourself with the styles of their questions, understand how to apply concepts rather than just knowing of them, and take as many of the AAMC practice exams as you can (preferably all of them).
Doing the above can minimize content review to ~1.5-2 months and spend the rest of the time reviewing test formatting and taking practice exams. I knew the concepts from my courses like the back of my hand anyway, so I did a little overkill with the content review. But since I knew it so well, I could easily apply the concepts come crunch time (actual MCAT score: 40+).
