If I may join in this offshoot of the main topic.
I think Barry is mostly right about long AV's but there are a few points to consider.
I don't think anyone should try to speak for everyone, only say "in my experience".
There is a world of difference between a single person watching a show on a PC or laptop and an audience sitting in a room. It's very easy to stop watching at home and there can easily be distractions.
The fact is people sit for up to three HOURS to watch a film. I know films are different o AV's but it does prove that it is possible to keep a viewer glued to the screen for a long time if the content is good.
On the down side to long AV's, even if each image was on screen for 10 seconds (which is a long time) then you would need 306 images to make a show of 51 minutes!!!!
Certainly my AV's tend to rely on a "trick", like one image slowly being revealed bit by bit, and once the viewer has got it then it can't carry on much over five minutes.
At our Camera Club we have one AV competition per season and it is called "Pieces of Eight". Originally it was called that because one member would put eight pieces of music on a cassette tape (that's how long ago it started) and people had to choose one and add their own images. We kept the name, after that idea stopped, and limited each entry to 8 minutes in length.
