You can add a formatting clause to the question like so:
FormAdd("Time", "00:00", "99:99")
Which forces the input to be limited to two number numbers, the ":" is locked into place and then two numeric numbers.
Nothing stops them from entering something like "44:45" for example, so you need to further qualify the input, and if invalid prompt the user to enter a valid time entry.
There isn't, yet, a way to prompt for an internal time input field - like what you see when entering time on a dialog - as the FormAdd() function wasn't upgraded to support that feature when the time input was changed. This feature may appear in a future update.