We spent about over two hours. It's quite lovely. It depends on if you want to look at what titles are on the shelves as well as the paintings, fireplaces and information. If I could have touched the books, I would be living there. It's not a large building. It's all about you and how long you'd like to take.
There's a Cafe and music in the lobby on Sunday afternoon and multiple rooms and exhibits and a lovely bookstore. You could spend 2 or more hours there easily.
It all depends on your style and how you like to move through museums. I went with a close friend. We moved through the museum at an enjoyable natural pace and before we knew it three hours had passed and there was still more to see. (Probably covered 90% of the museum).
About an hour. It's not a big building
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