Actual closing time of the Lecky Library

The TCD website and the plastic sign outside the Lecky library state the closing time on weekdays is 10.00 p.m.

The real closing time is 9.15 p.m. as that is the time staff begin to ask people to leave.

Why can the actual time of closure not be publicised? (whatever the reason for the early closure may be)

Also there is a sign on the notice board outside the library entrance, which is easily missed on the way in, which states that today the library will be closing at 9.30 p.m. I feel that this is disingenuous as it implies that this is some sort of exception to the norm.