http://microformats.org/wiki/h-event defined dt-duration as a stable property defined as the duration of the event. However, it does not show an example nor define a format.
hCalendar and iCal defined its duration property as an ISO8601 duration.
So, logically, the format should look something like: <time class="dt-duration" datetime="PT14M35S">14 minutes and 35 seconds</time>
http://microformats.org/wiki/h-event defined dt-duration as a stable property defined as the duration of the event. However, it does not show an example nor define a format.
hCalendar and iCal defined its duration property as an ISO8601 duration.
So, logically, the format should look something like:
<time class="dt-duration" datetime="PT14M35S">14 minutes and 35 seconds</time>
@snarfed argued(https://github.com/snarfed/granary/issues/169#issuecomment-546194496), however, that ISO8601 durations are rare in the wild and seconds was much more universal. This was in a media file context, however.