There's no real requirement for the International Date Line to be directly across the world from the Prime Meridian. IOTL we got lucky in that the world center of navigation (London) was directly across the world from a pretty nice place for a temporal discontinuity (the mid-Pacific). Even so, we've tweaked the IDL based on political considerations (most egregiously, Kiribati).
So you don't need a coordinate system based in eastern Australia to get a date line in the Atlantic. What would apparently be necessary is a situation in which trans-Pacific social ties are stronger than trans-Atlantic ones, which seems unlikely in a world dominated by Europe. The Atlantic crossing is a pretty natural route for development in such a situation.
So, bearing that in mind, here's my attempt.
The French Revolutionary calendar proves successful somehow, managing to take over all of western Europe, including Britain. Consequently, when eastern Europe adopts the Gregorian calendar, it does so in such a way that the Russian Far East (which, I suppose, could be better-developed ITTL to facilitate this) ends up on the same date as its neighbors in America. If the Revolutionary calendar then dies out--for my purposes, I hope in an east-to-west direction--we would have Europe and the Americas offset by a day.