Any update? I've seen the slideshow stop in just a few minutes sometimes BUT I'm using "Full Size" images. Using full screen slideshow, random images changing every 60 seconds (even tried every 10 seconds), transition time about 5 seconds.
I think your timeout for stopping it may be too short. Because the slideshow runs for the background image, we have to use good quality images. So they have to be large. Therefore, they might take time to come down even on a reasonble 3 mbps dsl connection. So it should just wait a looooong time before stopping the slideshow.
I urge you test on a slow connection like 512 Kbps connection equal to what you see on Edge networks on phones. If the slideshow can run for a long time (or for ever) on such a connection then your timeout would be long enough.