Hello everyone

I was just wondering how long it takes everyone to do an interview. I had an interview with a family yesterday and they were here for an hour and a half !! I tried hinting that it was time to go but I think they believe since I don't have kids I have all the time in the world. How long does everyone usually take to do an interview and what do or could you say to parents to make them leave? I don't want to be rude but I don't want to talk all night long either.
Please help!!