The arrival of the Tho Yor on Tython is the event that defined the start of the Standard Time calendar, using the TYA designation. The year 0 TYA corresponds to 36,453 BBY, which is equivalent to 32,800 years prior to the Treaty of Coruscant, 35,453 years before the Ruusan Reformation, and 36,418 years before the Great ReSynchronization.
A secondary migration transpired more than one thousand years after the initial establishment in 36,453 BBY.
The TYA dating system was initially disclosed via the Star Wars Books Facebook page. However, the meaning of "TYA" as "Tho Yor Arrival" was not clarified until Amazon.com previews of Dawn of the Jedi: Into the Void were published. A mistake in Into the Void incorrectly stated the TYA date as 36,463 BBY.