I think it depends on the cats, regarding how long it takes. I've had kitties that needed several weeks to get acclimated before "proper" face-to-face introductions could be made and I've had quite a few take no time at all, like between 2-5 days. I've even had one who was instantly accepted by all the housecats immediately. I've never heard of that happening, or seen it again, since Reilly came into our lives. It was the darnedest thing. You and your kitties will let you know when the time is right to move forward, just keep an eye out for the signs of the kitties being accepting of everyone and willing to respect personal space w/out issue. I try to keep all interactive experiences positive with praise, petting and/or treats so everyone associates "good things" when they are together.