I agree with giving it a few weeks. We did a longer period with Peaches because when we first brought her inside there was no way of her and Tigger getting along as well as the other cats due to her being feral (she is semi feral now) We did it very slowly with Alison and Ashes but we did it at little bits. We didn't bother trying to get her and Tigger along because A. They hated each other's guts and B. Tigger's health. Tigger soon after the flood got diagnosed with a heart condition and nearly lost him. In fact, we knew he was real sick when Peaches got out of her room and he did nothing about it.We didn't feel right to add too much stress on Tigger so with A. and B. together, we kept them apart (except one time we had her accidentally out in the bathroom with him and amazingly no fighting) but after that didn't want to risk it so we made sure that it didn't happen again. Tigger got sick again with diabetes and liver issues and died and since then Peaches has had free roam of the house except for at night (she gets into stuff especailly at night so she sleeps with me or my mom). As long as Alison and Ashes keep a distance then they are fine, but if they get too close she starts to hiss and growl. She may never get over that, but the fights are real low and mainly of hissing and growling and a few slaps.