I was soooo nervous the day got Honey neutered, but male rabbits are pretty straight-forward. I gave him his pellets in the morning before I took him in so I knew he had something in his tummy, just in case he didn't eat for a bit after the operation. When I dropped him off a brought a small bag of hay to leave with him and asked the vets to give it to him when he woke up, just so he had something to eat if he wanted. When I picked him up he was a bit groggy--I set him up with a blanket in his cage instead of the usual aspen shavings I was using at the time, and I made sure there was fresh hay and cilantro (his favorite) to entice him to eat. For the first day he did a lot of laying around. I didn't have a problem getting him to eat at all, and as long as you see poos in the litterbox, you know they're eating. After a couple days he was back to his normal self, though I didn't let him out of his pen for about a week to make sure he couldn't go zooming around. And he stopped his humping after just a couple weeks, though I know hormones can last a lot longer in rabbits even after fixing...I was lucky, lol.
I think females are supposed to take longer to get back to normal as the operation is much more invasive.