Most people say a half hour is good. But that should probly be the VERY least.

edit: Some people say it is, and that it's more sanitary. I would make sure he has LOTS of places to get his feet off the wire. Large piecves of cardboard can work. Or you can use wood. Once he is litter trained you could buy something that covers the whole bottom of his cage so he doesn't have to stand on the wire.

Ash