Try to find a cat with a personality similar to the ones already in the house. Kittens and young cats are more readily accepted than older cats. Most cats will feel that a kitten is something to be protected and cared for rather than regarded as a threat to their security. They may not like it at first, but should come around without too much trouble. Two to three weeks is about par.
Cats are also very sensitive animals.
They pick up on emotions and stress and as a rule, do not adjust well to traumatic changes in their lives. I asked the owner if there had been any recent changes or new people or animals in the house. She'd just been through a difficult divorce, which created a lot of stress in the household, the kids were confused and upset over it, they moved into a new apartment, got all new furniture and carpeting and had the cat declawed. The poor animal didn't know what was going on. Its life was in chaos and it was stressed, depressed, insecure and confused.