Some rabbits experience what’s called a “post-neuter craze” after a few days/a week after the surgery. Not all bunnies go through this, but a significant enough number. It means that any adverse hormonal behvior gets a lot worse than it was before the neuter. Incl aggression, territoriality, pee- and-poop-marking, humping, grunting, etc. This generally subsides after 2 weeks but the hormones are not quite gone from the system until after 6 weeks.
If you’re planning to let him hang out with a girl bunny, remember he will have viable sperm for about 4 weeks after the neuter.
Other than that, normal after surgery is of course a bit of lethargy after the anaestethic, he may feel cold and need a hot water bottle (but let him have enough space to move away from the heat source in case he wants to), you should serve him water in a bowl because a bottle may seem bothersome for him, you should entice him with delicious food so he starts eating, they don’t always feel very inclined to eat after surgery but rabbits must never get empty tummies. He shouldn’t jump or climb for like 2 days, you should inspect the incision-area daily. Don’t fast him before the surgery, rabbits shouldn’t fast, they can’t vomit so that’s not a problem during surgery.
I can’t think of anything else right now. But do ask more if you think of anything!