If you've got the time, Chronocalculator can add and subtract it.
It's a calculator made just for adding and subtracting time. Maybe you need to add up how many hours, minutes and seconds of music you want to record on a tape or a CD? Chronocalculator can make it easy to do that. Want to add up all the times you worked on a project? Well, you could use Chronocalculator to do that too. Need to do some weird science involving relativity and time travel that requires you to add and subtract time? Chronocalculator can also assist you with that.