Hi
The main property it seems that affects the rendering time is not frames per second but resolution. Change the resolution to the lowest value consistent with the AR. I found a 50 second mpeg4 clip exported in 2 minutes with a Highest quality option 720p but a low quality smaller frame output completed in 40 seconds.
Naturally mpeg4 image quality suffered greatly and the sound was simply awful!!! (IMHO I think there is a problem here)
Exporting as an avi completed perfectly in about 40 seconds as a 320 x 240 1fps file. So..try just using a smaller frame size.
Nat