Mine had absolutely no interest in my RBTA for almost nine months. I was actually talking with my girlfriend about trading them in for another pair that might. I woke up this morning and both of them were in the anemone!! Needless to say I'm pretty excited. But from what I understand its pretty much a 50/50 shot. Some do it, some dont.
As others have mentioned, it depends on the fish. It took my ocellaris clowns a little over a year. I'm convinced the only reason that they finally decided to go into the anemone was because I moved the tank into my new house. They got scared and needed protection.
Took about 6 months till mine took to it. They were in the tank first then added the nem about a month later. I think it was more by fluke though. I stuck my hand in the tank and they went scooting threw it and almost came to a complete halt when they went out the other side. Almost as if they really enjoyed it. cant keep them out of it now. lol
I have two black and whites and it's taken them 9 months and the female just started to go in my RBTA the other day I'm hoping both will be in and hosting it soon I also have a carpet nem that they don't even look at.