I'd take it in January of your junior year if you've gotten all the pre-reqs out of the way. That way you'll have winter break to study and won't have to contend with school.
Alright so let me break this down really fast...
Freshman*, Sophmore*, Summer before Junior Year- Slowly start to look into MCAT review, 1 Sem of Junior year*
*Do well in college, make sure to study, retain, and understand the material.
End of 1st Sem of Junior Year- During Winter Break study hard for MCAT
Beginning of 2nd Sem os Junior Year (~January)- Take MCAT
Withink 3-4 Weeks- Get Results of MCAT
Set up LOR and look into PS and list of EC's/resume
April/May- Send in applications to Medical School.
Senior Year- Finish any secondaries and attend interviews
2nd Sem of Senior Year- Hear if accepted
April/May- Make final decision of school
Fall after Senior Year- Attend first year of med school!!!!!
Does that look alright?