sjbd94 - every school is different, so you really will be best served by asking someone in your battalion. That having been said, my son's official Spring `12 schedule looked something like this -
PT - MWF 6:30 - 7:25
MSI Class - T/TH 9:45 - 11:05
Lab - TH 2:00-5:00
Rangers - T/TH - 6:30 - 7:30 + other random times
Unofficially, he probably spends about another 10 or so hours a week in ROTC-related activities - weekend extended labs for Land Nav, volunteering around campus, going to the range to shoot, working out, etc.
As an MSI, he was not involved in every activity that the MSIIIs were, but more than all the other MSIs since he was on the Ranger Team.
At his school, you can literally spend all of your time/activities doing something ROTC-related, or almost none of it. There are some who come to class and PT and do very little otherwise. Others are in Pershing Rifles (color guard), Running Club, and hold active leadership positions. It all depends on your personal preference, and your ability to manage your time.
My son managed to combine ROTC, Rangers, a STEM major, and competing at the professional level in sport outside school and was successful in all. Your mileage may vary, but good luck and enjoy the experience!