When it suits? Hows that?
From personal experience.
Booked time for box closing checked and verified, turn up 30 mins prior ready to take possession at booked time as stated in relevant notices.
Only to find box closed 45 minutes early after last train went early.
Signaller closed up and went.
Checked with on call personnel and could not get box reopened as work of low priority.
Job cancelled 10 men sent home, too far to deploy elsewhere in time.
I could see the page from the C notice through the window on the hook on the wall with the relevant item number highlighted.
Turned out the particular signaller had a history of closing early as he did not like staying the extra 15 mins past his time to deal with the possession.