The hours that the Library is open have changed. From now on the Library will not be open in the evenings at any time of the year. Instead, on the days the the Library is open, it will open at 12:00 noon rather than at 2:00 p.m. and close at 5:00 p.m. as it always has.
The reason for this is a change, over the years, in the visitation at the Library. Visitation in the evening hours has decreased to the point where there is little reason to keep it open and the requests for access before 2 p.m. have increased dramatically as more and more people wish to see the Library itself, in addition to accessing the book collection.
The new schedule can be found here.