I personally prefer to leave mine there earlier, that way, I know they aren't going to get in the food, and I dont have to listen to them pitifully asking for food and knowing I Cant give it to them - I have done it once with a later app for bloods and it was awful hearing her ask for food. My vet does ops between 10.30 and 12.30 though, unless they are having x-rays, as she has to take them to the other branch once she has finished, although Tigers x-rays were done around 12. And it gives them longer to settle before their op. I have to leave cats overnight when I use the rescues vet due to where they are and their opening times, and I hate that.