You can add or subtract two times. Four operators are provided: +, +=, -, and -=. The following example shows the use of these operators:
ITime Start(12:00), Duration(2:00),
Done=Start+Duration; // Done=14:00
Start=Done-Duration; // Start=12:00 still
Start+=Duration; // Start=14:00
Start-=Duration; // Start=12:00 again