Shift patterns in the Service can be a nightmare. If you work on a group of 40 staff, then it will cover a 40 week cycle, including
(E)arlies Start at 07:00, finish at lunch
(L)ates Start at lunch, finish between 20:00-21:00
(M)ain Start about 08:00, finish about 17:00
(A)ll day Start about 08:00, finish about 20:00
(N)ights Start at 20:45, finish at 07:15
This is an example, there can be many variations. If you don't like nights, you can generally swap them with someone, and you will be asked to work extra hours for no pay, but time off in lieu, (TOIL).
Whatever you work, it will balance out over the full cycle to 39 hours a week. After leaving the Service following 28 years, I wish you well, but would not swap places with you. If I can give you one piece of advice, don't think how you can change prisoners, think how they may change you!