Арифметические операции с timestamp

DATA:
      lv_time_stamp_sy TYPE timestamp.


CONVERT DATE  sy-datlo TIME sy-timlo INTO TIME STAMP lv_time_stamp_sy TIME ZONE sy-zonlo.

TRY.
    CALL METHOD cl_abap_tstmp=>add
      EXPORTING
        tstmp   = lv_time_stamp_sy
        secs    = -1200  "20minutes
      RECEIVING
        r_tstmp = lv_time_stamp_sy.
  CATCH cx_parameter_invalid_range .
  CATCH cx_parameter_invalid_type .
ENDTRY.