I'm thinking zero budget independent movies should top out at 55 minutes. An hour and a half is just too long. If you look at old Hollywood B movies, they run from 45 to 65 minutes. They knew what they were doing. Make your movie just long enough that people don't feel ripped off when they buy a DVD.
Look at books. They talk about how much people used to read. But books in the 1950s, when people read so much, were very thin. A 150-page novel was very common in those days. Novels now are four or five hundred pages. It's fine to give people their money's worth, but they have lives, too.
When my brother was in the band in high school, they would have these concerts that would drag on and on. Like the band director thought he was giving the parents a real treat when all he was doing was murdering their evening.
I've been watching some of the extreme low budget movies on Fandor. I like the idea of no budget movies, but I'm finding the actual movies a little hard to watch. Making them shorter would be a good start.