I'll just say that when I do this, I switch households between 5 and 6 pm on the last day of the term after the grades are in but before you receive them. I know that sounds precise but then they have earned their credits and finished their work. I usually have A-A+ students, so I'm picky about making sure they are fully done with the term. I rotate during that window and whenever I come back, I get asked to sign up for another term. If you want to "see the grades", you can save at 5 pm and then exit without saving after the grades are posted.
I just play it that they are all in school at the same time while they are there but I'm only following one household during a given term. I switch between households this way whenever I want and finish the university students when I want to. I have numerous different sims at uni living in the housing and I tend to play them during the fall, early winter, early spring or on either end of summer.
If you want to make it simpler, you could wait until they are done or send them to the same university in the same household in which case, they aren't rotational.