When using a time mask, it works when typing directly in the field, not when using the calendar.
For instance, if you don't require typing ":" to split hh and mm in the mask, you still need to do it in the calendar.
I also find handling times a bit hairy as we only have datetime fields behind the scene. So I use integers or nubers instead, but using a time format on them does not work.
Could we think of applying a time mask on a number/integer to allow duration entries displayed like time?
For instance, entering 02:30 would in fact enter 150mn or 9000s.