Factual error: In the lunch scene in the fancy restaurant with Frank Sr. and Frank Jr., the crystal goblets are of a pattern that wasn't available in the 1960's. The pattern is Mikasa Parklane, which I believe became available in the late 1980's.
Factual error: No airport in the world has runway 44. They are numbered 01 to 36.
Factual error: When Carl looks at a map over Europe, the borders of the countries are incorrect at the time: Germany is shown as one country, but it was divided into east and west in the sixties. Czechoslovakia was one country in the sixties, however it was divided into Czechia and Slovakia on the map, as it was at the time the movie was made.
Factual error: In the scene where Frank is tearing up Park Avenue in his "James Bond" sports car, a modern "NYC" lamp post banner is noticeable in the background.
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.