... the middle ages are perfect. King Arthur is somewhere in there, and HP has its early history in there, though LotR reads like it took place before the last ice age (and the map of Middle Earth almost looks like a pre-ice age map of Europe).

Perhaps you can add a couple of story ideas?

1--- Michael Crichton wrote a book, and there was a film of "Timeline", where a research group in the southwest US figures a way to go back in time to study stuff; it was poorly redone in the flick, claiming that a wormhole ONLY to a medieval period was possible.
2--- Myst, both novels and games, which seems to involve the far distant future when books, holodecks and dreams unite. You write a story, a thought-reading holodeck creates a world, you touch a panel in the book and are transported to the world, and the "resident AI" (artificial intelligence) of the world carries on without you over time, making assumptions based on your initial story assumptions.

When reading this group's premise, I thought of those two stories and wondered if someone at Hogwarts (Draco Malfoy comes to mind) snuck into the secret & restricted library, learned of the Myst linking books and screwed up his magic, interacting with the Timeline machine, which in turn causes time to get all wonky and...

The Story Begins.

Comments by group members welcome (and obligatory).