Well, I use the computers at Bethel University, they're only a few months old, and depending on the video length and compression it can take anywhere from five minutes to twenty. The videos usually vary from 250mgs to 900mgs once they've been compressed and edited. Just for kicks I let a video be exported at full quality, and it took about an hour to export and was three gigs! The new computers at Bethel could barley push the video without jamming.
In iMovie, here are my video compression settings that work best for me, and when uploaded to youtube, can be viewed in HD.
-Movie Settings-Compression: H.264
Quality: High
Frame rendering: Yes
Encoding Mode: Multi Pass
Dimensions: 1280X720 (1248X702)
-Audio settings-Format: Integer
Sample Rate: 48,000 kHz
Sample Size: 16-bit
Channels: Stereo (L R)
Hope this helps you out a bit
Douglas
New Brighton, MN
http://wc_sd45_7500.rrpicturearchives.net/http://www.youtube.com/user/SD457500