To calculate the time difference

FORM calculate_time_diff_in_sec USING before_date LIKE sy-datum
                                      before_time LIKE sy-uzeit
                                      now_date    LIKE sy-datum
                                      now_time    LIKE sy-uzeit
                                      time_diff   TYPE i.
  DATA: delta_date TYPE i,
        delta_time TYPE i.

  delta_date = now_date - before_date.
  delta_time = now_time - before_time.

  IF delta_date < 0.                   " irregular situation
    time_diff = 0.
  ELSEIF delta_date > 2000.            " avoid overflow
    time_diff = 0.
  ELSE.
    time_diff = delta_date * 86400 + delta_time.
    IF time_diff < 0.                  " irregular situation
      time_diff = 0.
    ENDIF.
  ENDIF.
ENDFORM.                               " CALCULATE_TIME_DIFF_IN_SEC