There are two phases; file creation, then upload.
The file creation process is indicated by a slide down sheet titled "Preparing Project...". It gives a slider and a text line indicating how long that process will take.
The upload phase presented in a slide down sheet titled "Publishing to YouTube..." and that says "Uploading movie..." also has a slider and a time remaining text line.
Is it one of those that is saying it will take 4 hours? If so which one?
The capability of your computer affects the first one, and the capability of you upload connection affects the second one. Still, 4 hours seems excessive. Are you using the very latest version of iM09? Mine is version 8.0.4 and works fine.
To eliminate a problem between iMovie and YouTube, it might be best to create your own file via the QuickTime export and then upload it your self. The easiest way to export is to use "Export Movie..." under the share menu. You mention HD, so choose that size option. Then connect via your browser and upload the movie.
A quick test indicates the exported HD format is a QuickTime movie with the following specs; H.264, 1280 x 720, Millions, AAC, Stereo (L R), 44.100 kHz. This is what the "Export Movie..." HD option will produce too.