I advocate keeping ALL cats indoors-only for their own safety, freedom from fleas and ticks, and your peace of mine in knowing they are safe. Some male and female cats continue to spray after sterilization; each is individual, so you will need to see for yourself how your little guy does. It takes a couple of months for his hormones to adjust and settle down. I would keep him inside for at least a week minimum, but again, I would STRONGLY suggest keeping him indoors-only. Thank you for being caring and responsible and getting him neutered -- he will be happier and healthier because of it.