Combination

   Combination time consists of an absolute time value plus or
   minus a delta time value. Combination time can use either of
   the following formats:

        "[absolute time][+delta time]"
         [absolute time][-delta time]

   You can omit the absolute time value. If you do, the delta
   time is offset from the current date and time. Whenever a plus
   sign (+) precedes the delta time value, enclose the entire time
   specification in quotation marks.