Delay between 2 times

CREATE OR REPLACE FUNCTION DELAY(ATA IN VARCHAR, STA IN VARCHAR)
  RETURN NUMBER IS
  DELAY;
BEGIN
  SELECT DISTINCT ROUND(TO_NUMBER((TO_DATE(sysdate || ' ' || '' || ata || '',
                                           'DD-mon-yyyy HH24MI') -
                                  TO_DATE(sysdate || ' ' || '' || sta || '',
                                           'DD-mon-yyyy HH24MI')) * 1440)) BULK COLLECT
    INTO DELAY
    FROM DUAL;
  RETURN DELAY;
END;
/