Left the group just before the movie started
From Zappa Wiki Jawaka
In 200 Motels, there are several references to the "fact" that Jeff Simmons "left the group just before the movie started". This seems to be a trick that Zappa or the band are playing on the audience; Simmons is in the movie, so he didn't "leave the group" before the movie was filmed, so it can only mean that he left the group just before the "movie" (likely intended to mean the theatrical performance of the film) started (whenever that was).
Or not depending on your point of view.