I think the understood conversion is that the "zero date" is January 1 of 1970 (the unix epoch and also the first start-of-year after the Tranquillity landing) being equivalent to Archimedes 1 of the year zero AT? This tool has it as the date of the moon landing, which makes for really awkward conversions I don't think most people would put up with at the changeover.

And then there's weird conventions about leap years. I wouldn't expect everybody to keep following Earth's particular exceptions to the 'regular' calendar. They'd switch to years of exactly 365 days sooner or later, but exactly when? 'AT day number' might be the only really universal measure.

Anyway there are thousands or billions of different calendars in use across the Terragen sphere. Furthermore, with the Wormhole network, there's only an approximate notion of simultenaeity. Two people can travel different routes from A to B, both experiencing less than a day of subjective time, and arrive years apart.

Given humanity's origin at Sol, the only monotonically-increasing measure of time for all locations in the Terragen sphere as a whole would be 'first light' at that location, or the time when the light emitted from Sol on 1 Archimedes AT 0 arrived at a particular location, minus the number of light years from Sol.

But this still does weird things to time when people travel 'instantaneously' via wormhole.

And then there's weird conventions about leap years. I wouldn't expect everybody to keep following Earth's particular exceptions to the 'regular' calendar. They'd switch to years of exactly 365 days sooner or later, but exactly when? 'AT day number' might be the only really universal measure.

Anyway there are thousands or billions of different calendars in use across the Terragen sphere. Furthermore, with the Wormhole network, there's only an approximate notion of simultenaeity. Two people can travel different routes from A to B, both experiencing less than a day of subjective time, and arrive years apart.

Given humanity's origin at Sol, the only monotonically-increasing measure of time for all locations in the Terragen sphere as a whole would be 'first light' at that location, or the time when the light emitted from Sol on 1 Archimedes AT 0 arrived at a particular location, minus the number of light years from Sol.

But this still does weird things to time when people travel 'instantaneously' via wormhole.