I am currently subtitling the first feature film I edited and the director as well as the producer insist that even if people speak continuously and two subtitles come one after the other, there should be a gap of even a few frames between the two captions. To me this seems like a weird jump, but I cannot find any guidelines regarding this. I tried to import Hollywood movies in Premiere in order to find out from the pros, but it's hard to find a Hollywood movie with printed subtitles to do that (premiere doesn't import srt). In your experience is my director and my producer correct or not?
There are no real standards for subtitles. It is mostly a matter of personal style weighed against what is readable to the viewer. Looking at movies, TV shows, and on-line content from around the world will demonstrate quite a range of subtitle styles and methods. Sometimes when two people are talking in a continuous steam the subtitles are back to back, no gaps. Sometimes one person is on one line and the other is on the line of text below them or the titles are offset to one side and the other. Occasionally, two different colors are used to indicate who is speaking.
The best thing to do is to complete a scene with subtitles the way you like (or do few variations) and have several people watch it with the sound off to see if the are able to read and distinguish each character's dialogue comfortably.