NROTC! Who's been through it?

It really depends on what college you attend. Some colleges only meet one day a week but it could be from like 14:00-19:30 or longer, and that is as an underclman. (It will be slightly more time once you become a junior). However, others have physical training multiple days a week, so you will not meet as for as long a duration on a single day. Also, at places like VMI or the Citadel, it will definitely be more intense than other places. At some places, you wear the uniform the whole day on which you have cles, others only during the cl.