I worked as a researcher (40hrs/week) and some other crap job (5hrs / week) as well as taking 25hrs/ week of classes in the summer. Its's called HELL.
I worked from 9am - 8pm everyday (45 min lunch), 7 days a week. THEN I started to study... I could never get more than 2 hours/day in... It's amazing how much time is spent on necessity tasks such as going to the bathroom, eating, bathing, keeping clean clothes etc. You will not have a life.
You better have some real dummies in your class.... thats your warning. Do you realize you'll be competing against students who consider it a rough day when they have to go to all their classes and only get 4 hours of pool and beer time that day? From my experience, medical school will take the boring guy with A's in the subject you listed over the guy who worked all those hours and got B's. Idiotic, but the way the game works.