Continuity mistake: In the scene where Frank's mother spills red wine on the carpet the stain shifts altogether once the next shot shows his parents dancing. (00:12:00)
Continuity mistake: When he pretends to be a doctor, and a he has to give advice on what to do with this patient, a woman gives him some kind of tool. He holds it in his hands, and towards his face, in a 'thinking' pose. Then the camera changes and the object is suddenly gone. The camera then jumps back to the previous position where he had the tool, but it's also gone in that frame. He's now just having his arms crossed.
Answer: It lasts several months. The stewardesses were juniors and seniors from the University of Arizona, whom he fake-recruited for a PR project for Pan-Am (they were not supposed to be real stewardesses, but dress like them and be photographed in various European capitols). Frank was frequently being asked where his "crew" was, so he thought it would lend him credibility.