As long as you have the pre reqs completed before you matriculate you're fine. You could even take it the summer before starting medical school, although I wouldn't advise that. Taking it your senior or junior year is fine. You don't need a lot of the o Chem lab knowledge for the MCAT, especially o Chem 2. A lot of schools are phasing out o chem 2 for biochem.
I highly recommend taking biochem before the mcat though