Students can have long breaks between terms. I assume if you play with aging on, there might be a limit, otherwise not. I always play a full rotation of my 60+ households between each term. The only disadvantage is they need to apply for scholarships for each term. If not taking a break, the scholarships will be valid for the next term, too.
Btw, it's not possible graduating in less than 3 terms. The only exception might be if the sim already has a degree, and attends Uni for a second degree, then some classes won't be needed, but it probably depends on what majors you pick.