6 months are recommended, that's how long the virus can survive outside the cat's body. And every object the sick has been in touch with (litter boxes, cat trees, toys, bowls) should be removed.

I know that's a horrible long time to wait... When I lost my Aysche from FIP, I waited 3 months before I got Katz (at that time, I wasn't very well-informed about the virus and the risks), and Katz did not get infected.

Kirsten