Timestamp Manipulations

REPORT  ZCA_ICM_TIMESTAMP.
 
data lv_dochd TYPE zins_dochd.
data lv_ts type p.
data l_tstamp_out type p.
 
select * from zins_dochd into lv_dochd where doc_id = '0000001000'.
 
  TRY.
  lv_ts = lv_dochd-UPD_TIMESTAMP.
  CALL METHOD cl_abap_tstmp=>add
     EXPORTING
        tstmp =  lv_ts
        secs = -21600
     RECEIVING
                r_tstmp = l_tstamp_out.
     CATCH cx_parameter_invalid_range .
                WRITE 'invalid range'.
                EXIT.
     CATCH cx_parameter_invalid_type .
               WRITE 'invalid type'.
               EXIT.
 
ENDTRY.
lv_dochd-UPD_TIMESTAMP = l_tstamp_out.
UPDATE zins_dochd from lv_dochd.
 
ENDSELECT.