Good to hear that you are now seeing the iPhoto videos in the Events Library - thank you for letting us know.
Each time iMovie is opened it will look for any new video clips in your iPhoto Library. If any are found, iMovie will ask if you want to generate thumbnails now or leave until later. I always let iMovie generate the thumbnails, rather than deferring it, as it doesn't take very long for these incremental updates. Yours took over 1 hour because it was possibly the first time iMovie had worked through the process.
You may wish to consider importing your video directly to iMovie Events, rather than first importing to iPhoto. It's more efficient to work with normal Events than with the iPhoto Videos Event, mainly in regard to organizing the Events Library. But then again, you may have a particular reason for importing video to iPhoto, rather than simply using iMovie for all your video.
EDIT: I mainly import iPhone video clips to iPhoto - just those sent to me by my daughter. It is a handy place to keep stuff that you haven't shot yourself, and which doesn't require editing. I've set mine up in iPhoto in a Smart Folder named Movies.
Message was edited by: John Cogdell