I don't know how I can optimize this SQL

Question

Dear ALL:
I don't know how I can optimize this SQL.
Is it possible to make a better SQL or PL/SQL?
Please let me know your good thought.
Thank you.
Sincerely,
===========================================================
(SELECT     A, B, C, SUM(D) as D, AVG(E) as E
FROM      T1, T2
WHERE     T1.timestamp BETWEEN TO_DATE('00:00:00','HH24:MI:SS')
AND TO_DATE('01:00:00','HH24:MI:SS')
GROUP BY A, B, C
UNION ALL
(SELECT     A, B, C, SUM(D) as D, AVG(E) as E
FROM      T1, T2
WHERE     T1.timestamp BETWEEN TO_DATE('01:00:01','HH24:MI:SS')
AND TO_DATE('02:00:00','HH24:MI:SS')
GROUP BY A, B, C
UNION ALL
(SELECT     A, B, C, SUM(D) as D, AVG(E) as E
FROM      T1, T2
WHERE     T1.timestamp BETWEEN TO_DATE('02:00:01','HH24:MI:SS')
AND TO_DATE('03:00:00','HH24:MI:SS')
GROUP BY A, B, C
UNION ALL
(SELECT     A, B, C, SUM(D) as D, AVG(E) as E
FROM      T1, T2
WHERE     T1.timestamp BETWEEN TO_DATE('03:00:01','HH24:MI:SS')
AND TO_DATE('04:00:00','HH24:MI:SS')
GROUP BY A, B, C
ORDER BY A ASC, B ASC, C ASC
===========================================================

Answer 1

Dear Warren:
Actually, for this query, it takes a few second to complete the query.
But, I have to create several time period and I have to optimize the SQL.
Time period is 1 hour, 30 min, 15 min, 5 min.
That is,
===========================================================
WHERE T1.timstamp BETWEEN TO_DATE('00:00:00','HH24:MI:SS')
AND TO_DATE('01:00:00','HH24:MI:SS')
UNION ALL
WHERE T1.timestamp BETWEEN TO_DATE('23:00:01','HH24:MI:SS')
AND TO_DATE('24:00:00','HH24:MI:SS')
===========================================================
WHERE T1.timstamp BETWEEN TO_DATE('00:00:00','HH24:MI:SS')
AND TO_DATE('00:30:00','HH24:MI:SS')
UNION ALL
WHERE T1.timestamp BETWEEN TO_DATE('23:30:01','HH24:MI:SS')
AND TO_DATE('24:00:00','HH24:MI:SS')
===========================================================
WHERE T1.timstamp BETWEEN TO_DATE('00:00:00','HH24:MI:SS')
AND TO_DATE('00:15:00','HH24:MI:SS')
UNION ALL
WHERE T1.timestamp BETWEEN TO_DATE('23:45:01','HH24:MI:SS')
AND TO_DATE('24:00:00','HH24:MI:SS')
===========================================================
WHERE T1.timstamp BETWEEN TO_DATE('00:00:00','HH24:MI:SS')
AND TO_DATE('00:05:00','HH24:MI:SS')
UNION ALL
WHERE T1.timestamp BETWEEN TO_DATE('23:55:01','HH24:MI:SS')
AND TO_DATE('24:00:00','HH24:MI:SS')
===========================================================
Do you know how this SQL is optimized?
Thank you,