The time when you let the kitty out of the room depends on the new kitty and whether or not you have other pets. If you have other cats, the new kitty should stay in its own room for at least a week. This room will then smell like the newcomer and the resident cats will be more apt to treat the room as the newcomer's territory. The new kitty will then have its own refuge when you open the door. If you're introducing the kitty to a home with a dog, particularly a dog that hasn't previously lived with cats, don't leave them unsupervised.
Dogs are much stronger than kittens and, even when playing, can inflict serious harm.
If you attempt to do so, your kitty will be even more fearful and distrustful of you. Give your kitty the same type of food it was receiving prior to adoption, at least for the first two to three weeks. Should you decide to change foods, slowly mix the new food into to old food in increasing amounts over a two- week period. Sudden dietary changes can cause unpleasant digestive upsets. If you still decide to let your kitty outdoors, wait until the cat is spayed or neutered, at least six months old and has received its full vaccinations, including rabies and feline leukemia.