Timing delayed overlays in Beamer.

You should be able to do transitions that appear/disappear based on time. I know the details are in the man pages for beamer, and I can't find teh website I used for doing transitions last year.
\transduration{40} works for frames (move to next slide after 40 seconds), can't recall if the objects w/i a frame have a slightly different name for their transitions.

So in short, a) what you want exists, b) tree doesnt remember it offhand.