Use INTERVAL
SELECT column_1, column_2, column_2 - interval '8' hour
FROM table_1
ORDER BY 3;
column_1 column_2 (column_2- 8)
-------- -------------- --------------
0 00:00:00.000000 16:00:00.000000
1 01:00:00.000000 17:00:00.000000
2 02:00:00.000000 18:00:00.000000
3 03:00:00.000000 19:00:00.000000
4 04:00:00.000000 20:00:00.000000
5 05:00:00.000000 21:00:00.000000
6 06:00:00.000000 22:00:00.000000
7 07:00:00.000000 23:00:00.000000
8 08:00:00.000000 00:00:00.000000
9 09:00:00.000000 01:00:00.000000
10 10:00:00.000000 02:00:00.000000
11 11:00:00.000000 03:00:00.000000
12 12:00:00.000000 04:00:00.000000
13 13:00:00.000000 05:00:00.000000
14 14:00:00.000000 06:00:00.000000
15 15:00:00.000000 07:00:00.000000
16 16:00:00.000000 08:00:00.000000
17 17:00:00.000000 09:00:00.000000
18 18:00:00.000000 10:00:00.000000
19 19:00:00.000000 11:00:00.000000
20 20:00:00.000000 12:00:00.000000
21 21:00:00.000000 13:00:00.000000
22 22:00:00.000000 14:00:00.000000
23 23:00:00.000000 15:00:00.000000