I just finished Baxter and Pratchett's The Long Earth -- it was pretty good; I'll have to see if I can get my hands on the sequel(s). Having noticed that many of the events and diary entries in the book have been carefully dated, I wonder if the authors included a specific date for "Step Day," the day that the plans for the Stepper (a device that allows travel in between worlds) were posted on the internet, and many people disappeared, permanently or temporarily.
I do recall that certain events are dated by the number of years since Step Day -- if I remember correctly, Sally steps off from the Datum (the version of the Earth from which humanity comes; our Earth) on a precise (10 year?) anniversary of Step Day.
Is a calendar date given for Step Day?