From film + at + 11, where "11" means 11 o'clock. This phrase originated from the television news broadcasting industry, where the late evening news is traditionally broadcast in 11 o'clock.
"film-at-11." YourDictionary, n.d. Web. 17 August 2018. <http://www.yourdictionary.com/film-at-11>.
film-at-11. (n.d.). Retrieved August 17th, 2018, from http://www.yourdictionary.com/film-at-11