The more frequently you study, the more effective the studying will be in my opinion. It'll aid in reinforcing your neural pathways.
Personally, I already started studying last month in preparation for the April '04 MCAT.
I have a regimen designed for each week, stretching from now to April. I will be spending 5 hours a week reviewing topic material from chem, o-chem, bio, and phsyics. For instance, last week was devoted to chemical kinetics (gen chem), aromatics (o-chem), and reproduction (bio).
During my winter vacation, I will take a diagnostic MCAT to determine where my weaknesses lay so I can take remedial action. I'll also begin working on timed writing samples.
For the month prior to the MCAT, I will take a practice test every weekend to help develop the 'speed skills' that I'll need on test day.
I know it seems very anal. But it reminds me of the old joke, "How do you eat an elephant? ONE BITE AT A TIME!"
GOOD LUCK to all of my future medical colleagues!