ALTER SESSION SET NLS_LANGUAGE=english; -- First day of week
SELECT
    -- Last Sunday of October at 02:00
    NEXT_DAY(LAST_DAY(TO_DATE(TO_CHAR('01/10/' 
        || (EXTRACT(YEAR FROM SYSDATE)-5 + level) || '02:00:00'), 
           'DD/MM/YYYY HH24:MI:SS')) - INTERVAL '7' DAY, 'SUNDAY') AS H_WINTER,
    -- Last Sunday of March at 02:00 (missing hour)
    NEXT_DAY(LAST_DAY(TO_DATE(TO_CHAR('01/03/' 
        || (EXTRACT(YEAR FROM SYSDATE)-5 + level) || '02:00:00'),
        'DD/MM/YYYY HH24:MI:SS')) - INTERVAL '7' DAY, 'SUNDAY') AS H_SUMMER
FROM DUAL CONNECT BY level <=10;