=str timed and timedIntervalBetween on Duct[I, O]

Same as the Flow.timed ops, but defined on Duct.
Not happy with the amount of duplication, but I have a way simpler case than @drewhk, since they would be expressable together if there was a "Transformable", that both (Flow, Duct) would implement. Not sure if thats something we want to do now though - opinions welcome, otherwise we can get it in duplicated and find something more general afterwards.

Timed ops need Java API still.