The forms for the manual adding and for the editing of time entries have been over-worked functionally: By default, an option is now activated which interlinks the start and the end time with the duration. A change of one of the fields causes automatically a change in one of the other fields so that the duration can always be calculated from the times.
If you exceptionally want to add a time with a differing duration, you can unlink the fields from each other. In order to do that, you'll find a link symbol at the duration field.
The form in our stop clock and the apps will get updated shortly!
Update 21 September 2016: The web version of the clock has already got updated.