Expect at least 6 hours/week of time committed to yell like hell until homecoming. IIrc, practice is 8-10 p.m. or 9-11 pm Tues, Thurs, and Sun. All your time practicing yell like hell will be well worth it if you get to paint up for semis and finals (especially when helping to paint up the sorority girls you're paired with.) Chances are you'll also have at least an hour chapter meeting every week and at least an hour of new member/pledge education, as well as time for household chores (which could be more for new members than associate members.) Most houses also have required study hours, so that would probably qualify as fraternity time, but will also be time you are studying.
You can put a lot of time into Greek stuff if you want to, or you can spend the majority of your time playing halo in your room chowing on cheetos and slurping mountain dew, same as wanting to/not wanting to get involved with the majority of social groups/clubs at ISU.