We haven't encoded duration for any of our recordings in collections, but I
thought I'd alert you to a compilation of EAD encodings of audiovisual
material I created last year. You can look at it here:
There's a lot of variety, and few of the examples include duration at all.
There's an interesting use of <dimensions> from an Italian repository,
<materialspec> is an interesting usage though. If you'd feel comfortable
sharing what you end up with, I'm looking to expand my "EAD for AV" document.
Archives of American Art