You've already figured out the biggest tip I could give you, don't use bikes on either campus to get to class! In addition to that, there actually is a get to school early animation, but I usually only use it for their first class of a term to figure out in which building each class is held. But I don't let them leave on their own from the dorms, ever! After that, you only need to get to the Commons for either school around 40-45 minutes before class starts.
Anyway, here's what I do and it hasn't failed me yet with two students both who have graduated with an A+ GPA and honors for their degrees:
1. First class of a new term, send your Sim to either of the Commons lots, depending on which University they are attending an 1-1/2 hrs early. Once the clock runs down to an hour before class, they will head to the correct building on their own so you know where to go for the next class.
2. For all classes after the first class, send your Sim to the Commons 40-45 minutes early and then click on the ground in front of the building for their class choosing 'walk here'. They'll walk there and be ready to go when it's time for class. Most of the time they'll be early enough to do some things to fill needs if you wish instead of just standing there waiting; do homework, call a friend, eat a harvestable, play some games on their cell, etc. Just be sure to stop whatever they're doing a few minutes before class to give them time to stop and disappear to go in the building.
I hope this makes sense and helps! :)
EDIT:
* Note - This method was used with Sims who had no autonomy. I'm a micromanage freak. lol I don't know if it would work for Sims with full autonomy. They might try to run off and do something else and you'd still be late. Worth a try anyway I guess. *shrugs*
Good luck and Happy Simming! <3