I have always kept my guys in for a month, even Misha who never wanders further than 10 foot from the house. Its best that they are 100% settled in their new house. Then I let them out in the garden for a quick 10 mins on and off throughout the first day and go out in the garden with them, I then make it half an hour, then an hour, gradually getting longer and longer till the first brave cat goes over the fence - then I wait almost in tears till they return.
Basically I have found when I first let the cats out they will do a recci of the garden perimiter smelling and leaving their scent everywhere - once I see them do this I can settle a little more as they are territory/home marking.