You should take the MCAT when you can kill the MCAT. Any input you receive on how other people do it should be taken seriously only if it applies to you.
What I suggest:
1. Go take a practice MCAT, yes I mean now, at www.e-mcat.com
. Just take the verbal section, without doing any prep. If you score 10 or more, then you have reason to believe your base of general education is sufficient to predict success on the science sections. If you score under 10, then assume that you're starting at a disadvantage and that you'll need to take on MCAT prep full time for a minimum of 3-6 months. (It's not this black & white; I'm throwing down a gauntlet here.)
2. Then don't think about the MCAT again. Get A's in your prereqs. Do whatever it takes to do this. If you have to sacrifice volunteering and other EC's to get killer grades, that's a sane tradeoff. There's not much that's more difficult and time-consuming and slow-death-by-compromise-inducing than GPA repair. While you're getting A's, actively recruit recommendations from your profs.
3. WAY down the road, after you're successful in a whole bunch of prereqs, figure out a schedule that works backwards from a June 1st. You need to have all your ducks in a row on June 1 of your app year. Your MCAT date can be no later than early May. Take another practice test (with some prereqs finished) and see where you're at. Make a rigorous prep schedule (tons of examples of these in the MCAT forum), stick to it, take every practice test there is, pay money for a course, and take the test once
. (Retake prep down the road is demoralizing, cost-ineffective and inefficient.)
Best of luck to you.