A calendar reveals a lot about itself by where it chooses to stake its first day.
A Human rises to speak and live and ascend with conviction against greed and apathy, and his impact upon the world is so great that a new calendar divides time into everything before his birth and everything after.
By the measure of his calendar, it is 3813 GS.
A Verin rises from the dead with vengeance in his heart. By force of will breathes Meta into the world. Without him there are no souls, no Monoliths. And so a new calendar divided time into everything before his death and everything after.
By the measure of his calendar, it is 14576 KS.
A Sazashi rises to stand against her creators. Their lives are created and extinguished without regard, and their only freedom comes from revolt towards a shared cause and a unified vision. She was their great voice of hope, and so a new calendar divided time into everything before her war and everything after.
By the measure of her calendar, it is 5939 LJS.
Other standards exist. Hundreds on Eden alone. Some measure by the moons, some by the farms, and some by the phases of the suns. And so it is on Jhoutai as well. And so it is on Anchaemo as well. And Perduro. An so on. And so forth. Except on Victoriana, which is very precise about such things.
The Narrator measures Ethnis by everything before its first point of lore and everything after. For the Narrator, this means the first anthropological events of the Verin.
By the measure of that calendar, it is 21156 CS.
Ethnis Hubstandard Time (EHT) is based on the timescale of Jhoutai. It is the time standard by which the rest of Ethnis orientates itself. For the sake of all official business, this is the gold standard, even among Banners which dislike the Pact. This is because the standard was adopted before the Bannercasting, and so became the heartbeat by which the universal economy survived.
Today, all EHT clocks can be synced to the Æthernet to validate its time against the clocks of Jhoutai. This allows all times to compensate for local temporal distortion, as well as making it possible to keep EHT even in environments without local celestial bodies that can be used to calculate a similar time, such as surviving on extremely alien worlds or on space stations.
Despite EHT being the standard, most worlds will develop a local time based on local orbit and celestial features. For example, the world of Kytheria marks its "day" cycle by the orbit of its moon, Thalia, which has a 12 hour period and thus lines up most closely with the circadian rhythm of the common Sophont, despite the fact that the sun, Apollo, has a 72 hour period.