hi
I used Min to initiate the program and to find the smaller hour within different rows in the column XXX
like this
I have

XXX
AT230 12:00 11:00:00
AF1457 14:00 13:00:00
16:00 15:00:00
18:00 17:00:00
20:00 19:00:00
22:00 21:00:00
00:00 23:00:00
02:00 01:00:00
04:00 03:00:00
12:00 11:00:00
14:00 13:00:00
16:00 15:00:00
18:00 17:00:00
20:00 19:00:00
22:00 21:00:00
00:00 23:00:00
02:00 01:00:00
04:00 03:00:00