Tom
Tom asked Genevieve Cogman:

Are the worlds in the library multiverse all on the same time as each other? I.e If you were to go from London in Vale's world to Kai's Uncle's (if it existed there) then it would be the same day and year (accounting for travel)?

Genevieve Cogman As far as the Library knows, it would be the same day and year.

However, different worlds may have different calendars and different climate conditions, and be at an "earlier point" in their history. So hopping from Vale's London to the London in the world where Ao Shun likes to hang out on the same day would be feasible, but whether it was the same calendar date (day, month, year) would depend on whether both worlds happened to be running on exactly the same calendars. This can cause problems.

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