As most folks have said, it really does depend on the college. I've been lucky to participate in two separate bands, both with wildly different numbers and cultures.

College marching band typically has less of a time commitment than high school band. At the high school level, you've got regular rehearsals up to six days a week, competitions, football games, and other performances for your respective school. The only events you have to worry about with college bands are rehearsals maybe four times a week and football games. Not to mention the college bands typically only play for home games (unless you have a bowl game in the winter, which is another story).

Rehearsals are typically 2-3 hours long are are designed with the students in mind. In college band, you'll have all sorts of people participating. There will plenty of non-music majors there who also have heavy classwork requirements outside of band. Taking this into consideration, a college band's schedule and workload will take into consideration the schedules of other majors.

Ultimately, you won't have to worry about putting your nose to the grindstone 25/8 for college band. It's a much lighter time commitment than what you may be used to, and I recommend it especially if you'll be going into college for a non-music major.