Improvements

First of all I dont think you should have to put the colons in. It should automatically add the colons for every 2 digits (except in the hours column) Similarly - to type in :10 seconds plus :10 seconds should NOT require you to manually type 00:00:10 plus 00:00:10. When you only type :10 it should know you are referring to seconds.

AWrinkleInTime about Time Calculator, v1.5