I graduated from there May 04, so any info I can give is a bit dated, but may still hold true.
JU and San Diego have the largest ROTC units in the country, but it goes back and forth over which is the largest. Typically we PT'd twice a week in the early morning and on Thursday's we wore khakis to class and drilled in the afternoon. You'll be expected to participate in some of the events like the drill team or the pistol team. They try to do a lot of fundraisers so that they can send the teams to competitions without anyone coming out of pocket. As a GM, you can expect to be asked to be on the pistol team, and as a prior, you can expect to be asked to drive the team to a competition. The ROTC unit has a van, and the skipper always wanted a prior to be the one driving the teams around. Don't think of it as a bad thing, especially when it's time for the drill team to go to Tulane!
Over the summer, most of the ROTC guys do summer cruises so the unit is very small. We'd PT once a week and that was about it.
Otherwise, you're just a full time student.
As far as how the MIDS and OC's like it, that changes every semester when someone new takes over the unit.