It was still pretty normal in Britain in the 70s. As a kid I remember watching the end of some disaster movie before it went back to the beginning - most likely Airport '77 or '79/'80. It started to change in my (relatively) small town with Star Wars, Superman and Raiders, when at least some performances required standing in line on the street and waiting to be let in at the right time (nobody had dreamed of pre-booking, or seat reservations, at this point). During the transition period newspaper listings would specify "cont.perf." for continuous performance to indicate when the old system was still in play, which carried on well into the 80s.

Edit to clarify: they did generally list the times that each showing would start, so you could choose to arrive at the beginning and leave at the end. But nobody was forced to do either. You could arrive in the morning and watch the same film five times in a row, if you wanted. Or two films alternating, if it had a B-movie showing between the main film... ah yes, fond memories of strange B-movies like a documentary around offshore oil production - perhaps due to the time period when movie studios became just one part of massive industrial conglomerates, perhaps because they wanted to bore the audience into leaving and freeing up seats... also the combination of Airplane! with the execrable Sgt Pepper's Lonely Hearts Club Band (Beatles jukebox-musical starring the Bee Gees).