There was a short story I read years ago.
A man stumbles across a strange library in a mist, or perhaps he got lost in the stacks of a library, I don't remember. But the library has all those books that could have been written that never were, e.g. plays that Shakespeare could have/would have written, but never did/got around to, things of that nature.
The man has one hour or maybe the rest of the evening to roam the stacks, after which the library vanishes forever. Ring any bells?
Sounds like The Fort Moxie Branch by Jack McDevitt. An author discovers a transdimensional library that collects the works of great authors that have been lost to history. Worth reading.
Could this be Nelson S. Bond's "The Bookshop"?
An unsuccessful writer discovers a bookshop which has unknown books by Shakespeare, Dickens, Doyle and many others, and by a dead friend of the writer (he recognizes the title of this book as something his friend had talked of wanting to write), and most importantly, the book he himself had always meant to write.
He is not allowed to take anything out of the shop, and when he runs out - with the book - he is run over, and passers-by see only a book with blank pages.
You may be remembering the snippet “dans un bureau” by David Madore. It's not a good match though. There's no library, only a home the narrator visits, and they are already in a universe where those works of art exist, they're nonexistent only from the point of view of us readers, and there's no indication that anything would disappear in an hour.
