To me, being on time is a show of respect. I respect our agreement to meet up at an agreed upon time so therefore I make an effort to show up on time or a little early. Some times life happens which makes you run a little late which isn't a big deal if the other party understands and you don't do it frequently.
In the situation with your friend, it sounds to me he's over committed himself or he at least feels that way. He's going to graduate school, working and still attending social gatherings. That's pretty difficult to do all at once. I'd probably ask him to list out everything he's doing and ask him what he needs to do and what makes him happy to do. Then find some way to prioritize between everything.
This advice is based on my personal experiences. My wife and older sister both happen to be chronically late people. My dad and I both happen to be people who hate to be late to where we'll show up early to avoid being late. With my older sister, we got to the point where we'd tell her that the family event started earlier to get her to show up on time.
With my wife, she is late to everything from friend's parties to doctor's appointments. I noticed that two big things:
- My wife would overcommit herself. My wife would cram her schedule full of stuff to "optimize" her trip outside, but there wasn't enough buffer between events to get to everything on time. She'd be late to the first event and that lateness would domino to the other events. Plus she'd be just exhausted at the end and dreading the next trip outside.
- My wife had these rituals that had to be completed before she could leave the house such as she'd have to eat a home cooked meal AND do all of dishes before she could leave.
Through the years, I helped her target these areas. I helped her spread her obligations out more e.g. it's not a good idea to see 3 different doctors in 1 day in different cities. I convinced her it's better to show up early to a doctor's appointment, because sometimes they can squeeze you faster than showing up late and hoping they squeeze you later. It's just a more pleasant experience to be on time. We're not stressed out about being late and the doctor's office isn't stress out and angry either.
For her rituals, I introduced her to protein bars and snack bars so she could eat something and not generate any dishes. She's even gotten to the point where she's okay leaving some dirty dishes behind.
She's still late to some things like gatherings with friends, but she's gotten much better at showing up early or on time to important commitments.