The vet is just covering his back. There is a saying that smaller the beast higher the risk, this is due to their capacity to deal with the anaesthetic, but as long as your vet is good and experienced with bunnies it should be fine. Cheeko was home in a few hours and right as rain after a couple days he was only a few months old though but I think its only females who are more complicated the older they are, with boys its just snip snip regardless of age I think.
Another thing, I made sure my bunny had priority, this has been his house for 5 years after all, everything was new for the kitten so it was her who had to get used to him. I made sure he felt safe and secure and also in control of his space, the kitten has had to learn who is boss! I did this as I think cats have more chance to injure a bunny than vice versa so if she accepted him as boss I was limiting possible conflict. Seems to be working so far anyway.

__________________
Proud mum to Tiffany, Bellinda and Jessica