Neuters are easier on a rabbit than a spay, but your bunny may still need some pain meds for the next couple of days. What they give him at the vet will be good for the first day. You don’t fast a bunny before surgery. Sometimes a receptionist at the vet will tell you that, because they are used to saying that for dogs and cats. Make sure that you have all of his favorite veggies/greens on hand after he comes home, and some favorite fruit too, in case he isn’t eating much when he gets home. If he is on pain medication, that will keep him quieter than normal, which is good, since you don’t want him to be racing or jumping around the first few days. Make sure that he isn’t chewing on his stitches, otherwise he will have to wear a cone/collar. Those usually make rabbits pretty miserable, so only use one if you have to. None of my bunnies, whether male or female, have tried to chew their stitches or overgroom the surgical area. He will probably bounce back pretty quickly. Just make sure that he is eating well and pooping normally.