HayleyRose and Lut, both of you were introducing a kitten. Adult to adult is usually different. I think I only had 1 cat just waltz in here and make herself at home without any problems. All the others had a time alone first. (Guinness will have this any way because of not being tested). Now, the amount of time seperate will depend on their reactions to each other. The best thing is to be available to observe them and you will know when they can be trusted with each other. Hopefully it will be right away.