Rebecca-
Is he staying overnight at the vet or sending him some same day? It seems like most vets send home same day- but I have heard some owners mention that there bun spent the night- more so for spays than neuters, I believe.
Neutering is usually quicker and less invasive than a spay- a spay is much more of an abdominal surgery- and that is why the boys usually bounce back quicker than the girls do.
Expect that when you bring him home that the vet will want him kept quiet- and you can offer food to tempt him to eat again- usually they will eat their favorite greens first, hay and then pellets. It can take a day or 2 to get them back into normal eating routine and normal amounts of what he usually eats. It is important to keep him less active to give the incision a chance to heal, and to keep him in a temp controlled environment after you bring him home- as anesthetic can affect the bodys ability to regulate temperature- you don’t want him too hot or too cold- just what he is usually used to inside the house should be fine.
Usually the vet likes you to check the incision at least once to twice daily to make sure it is healing well and the bunny is not licking excessively and preventing it from healing (saliva/licking inhibits healing).
Make sure not to fast (remove food) before you take him in for surgery- this is normal to do with dogs and cats as they might vomit- but since bunnies do not vomit and have sensitive GI tracts it is important to keep food moving thru his system- so no fasting before surgery and get eating again as soon as possible after surgery. I took some greens and a treat or 2 with my bun when she was spayed so it was offered to her when she woke up. Mine would not eat immediately after waking up, she did not eat until I brought her home that afternoon- but others have reported their bun willing to eat at the vet after waking up.