When your sim leaves early for class, they will go stand in front of the building that that class will be held in.
Each campus only has 2 class buildings. At Britechester, most of my classes seem to be in the big building, and usually only electives would be held in the smaller one. No guarantee there though. At Foxbury it seems to be evenly divided.
In my game, I have time slowed down using MCCC. Many activities take a set amount of game time to complete, but I waste a LOT less time walking around. Even when I have a non-spellcaster who also refuses to run, my sims can get to class in 10 minutes.
Also, since you're at UBrite, the campus is a lot more bike-friendly. A bike will hopefully get you around faster. Foxbury's campus is stairs all over the place, so bikes don't work out very well.