Alfred Hitchcock? George Bernard Shaw? Apocryphal?

Question for Quote Investigator: Enthusiastic critics treat films as elevated objects of art, but the famous director Alfred Hitchcock once insightfully remarked on the pragmatic limitations placed on commercial movies by human biology. He stated that the proper length of a film was dependent on the endurance of the human bladder. Would you please help me to find a citation?
Reply from Quote Investigator: In 1963 “The Oregonian” of Portland, Oregon published comments made by Alfred Hitchcock during a phone interview. Emphasis added to excerpts by QI:1
Motion pictures are the only form of entertainment where the audience is forced to sit quietly for two or three hours without interruption, Hitchcock continued. In theatrical terms, television is superior in this regard to motion pictures. The hour-long show is broken into three acts because of the commercials.
“Wasn’t it George Bernard Shaw who tried that noble experiment in one of his early plays? He tried to discover how long the first act could run, based upon the endurance of the human bladder. I wish I could recall his conclusions.”
On this occasion Hitchcock spoke on the bladder theme, but he did not utter a synoptic remark that would fit into a book of quotations. QI is unsure whether Shaw actually wrote or spoke on this topic.
A year later in 1964 Hitchcock traveled to San Francisco, California to shoot a scene for the film “Marnie”, and he communicated with a journalist working for the “San Francisco Examiner”. Hitchcock said that the running time of “Marnie” would be less than two hours, and he opposed overly-long films:2
“If it’s a compelling story, you want to read it at one sitting. The novel can be put down and picked up again. The play is divided into three acts. But the movie should be quick, terse and all of a piece.
“I think it was Shaw who advised young playwrights to gear the length of each act to the endurance of the human bladder.”
Below are additional selected citations in chronological order.
Continue reading “Quote Origin: It Was Shaw Who Advised Young Playwrights To Gear the Length of Each Act To the Endurance of the Human Bladder”