Result is the duration obtained by subtracting duration2 from duration1.
Durations must be entered in the form: P1Y2M3DT04H05M. Periods can be made negative by using the minus character before the P designator, e.g. -P1D.
P is the period designator, and is mandatory; the rest of period is therefore:
1 Year, 2 Months, 3 Days T(ime designator), 04 Hours, 05 Minutes.
The example shown below, subtracts 1 hour from flighttime, i.e. PT1H.