Can't address multi-day time
This is a basic time calculator for adding and subtracting hours only. I was a disappointed the app can't deal with local time calculations. For example subtracting 2:00 from 01:00 give a result of -1:00 not 23:00. Adding 2:00 to 23:00 gives a result of 25:00, not 01:00. I was hoping to use this to manually calculate itineraries across multiple times zones and UTC dates, but it can't address multi-day time.