I like having classes between 20-35 minutes. It really depends on the class. If it is something like HoM it seems like forever (pls don't hate me, Max, it's just my opinion on History) but if it is something I enjoy, like Charms or Potions, I want the lessons to last a lot longer.
I enjoy it more when there are interactions. I hate it when a Professor spends about five minutes on the rules and questions, then they just stand there and copy-paste a whole blob of text. This makes lessons a lot more boring, and I don't want to spend a lot of time in those ones.
I would enjoy it if the teacher actually interacted with students. I love it when in Flying if we're all good we get to play a game on our brooms. Or, in Charms, if we're good we get to learn a new spell. I also enjoy when they ask quiz questions during the actual lesson. Example: In Charms if we're talking about Mimble Wimble, and he asks if any of us know the inventor.
This is just my opinion