It can sometimes take a while, for my cat Cleo when I first got her she adapted really quick, but she was only about 1 or 2 months old. For some cats it can take up to 2 weeks to a month. They just need to get used to their new surroundings.
In this past month I have lost 3 of my Outside cats. Two tortie, Patch and a kitten I had yet not given a name yet but I called her Pretty as a nickname, and a black kitten named Duke. Even though I have been through this many times before, but it always make me sad to see the careless people...