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.