There really is no "good time" is the shortest answer, just to pick the least ****** one.
Because you're a science major, you have to study. There really is no "light science" course load. Which means EXTREMELY disciplined all the time. No partying a couple times a week. No going to the gym instead of studying. You are studying for the MCAT and your regular courses and maintaining your ECs. Nose to the books basically all the time. It can be done.
I took a large course load (4 sciences and 2 non-science classes) while "studying" for the MCAT because I thought it would be a good prep for what med school would be like (work wise) but it came down to this:
-My grades suffered (my avg gpa was >3.95, got a 3.70 this past semester, probably going to look bad that my grades declined before applying)
-I didn't have enough useful brain-time to devote to MCAT (You might have time, but you can't be burnt out)
-Lost some weight cuz I wasn't at the gym as much
-Was stressed out 24/7 that I should be doing something more useful which makes it hard to have fun believe it or not even when you're doing something you usually love to
So, finals ended which was rough studying for 6 finals, but luckily they were spaced out. Then had 2 weeks to study for the MCAT.
This was all my Junior year. If I were you I would take the MCAT during summer sophomore year (when you can still retake and be fine for the "correct cycle") which it seems like you are doing based on the courses you listed (typical sophomore pre-med science classes), but the only downfall is you WON'T have biochem or physiology, which you will learn in your prep class but I think "classroom" exposure to the material first makes studying 1000x easier. My advice would be to take the MCAT June or July and only study when you get out for summer break. This will let you do a few things, like go to the gym, have fun once in a while etc, because you're not spending this time on other stressful stuff like classes. This will let you get the highest score (IMO) that you really deserve on the MCAT.
This coming from me who will probably see an MCAT score below my potential when I get my scores back soon, just because I was so burnt out from classes and then studying for the MCAT.
My pre-med adviser told me to not show weakness in scheduling (ie- dipping from 19 credits/semester to 12 credits during my "MCAT" semester) because it would show that I couldn't handle a medical school work load, so 12 might be a little too light.
Even with Orgo and physics, I think Orgo was easier than gen. chem, and college physics 1 and 2 are actually pretty easy but both of these classes require library time, bio chem is a lot of work though and a lot of memorizing but I think it will help you with the MCAT. The research class too will probably be a lot of work.
In short, I don't think effective MCAT studying could be done during this semester, even though it is only 12 credits. Unless you are 100% efficient and 100% disciplined (which unless you are a machine and unlike 100% of college students everywhere, couldn't be done.) I would say take the MCAT class, learn in the classroom but don't kill yourself trying to study for a May date. Take your finals, take a few days off to just veg, then study hardcore for a June/July/August date and apply May 2012. But don't work during this time, or work a lighter schedule. By postponing until July you can allow yourself to go to the gym, go out with friends etc, while still studying for the majority of the days.
IE- your life won't hiccup as much as if you were to do it during the semester.
And coming from me, and someone else who already applied- studying for MCAT during any semester completely sucks. So, take time to study (It might not be best case scenario, but it will improve your score) instead of hastily rushing into taking it because you want to apply early (like me). Guaranteed your score will go up (which matters more than when you apply IMO, but I don't really know for certain)
From what you're saying, it sounds like you're a freshman going into sophomore year, so this is my advice, stuff I wish someone had told me.