I'd like AllVideos to pass along a start time for a particular YouTube video, as you would get using something like www.youtube.com/watch?v=eLIXnWg59Wg#t=26.9 . I've tried just including "#t=26.9" along with the video ID, but when I do that the video doesn't come up at all. Is there a parameter or something I can include in a {youtube} tag to make that happen? It  would sometimes also be nice to set a stop time.

Hi. No this feature is not available.

You could use the Youtube Player tools to do it. There is a fairly wide range of customisation aavailable and you can pick up the amended embed code here: developers.google.com/youtube/youtube_player_demo