Archetryx was a planet with temporal shields (powered by gravity wells) which kept the planet a minute ahead of the rest of the universe. It was located in the same system as Etra Prime.
Archetryx was host to the treaty attended by twenty of the Temporal Powers. At the time, the Daleks returned Etra Prime to the universe on a collison course with Archetryx, resulting in the Etra Prime Incident. The planet suffered extreme damage, but there were survivors. (BFA: The Apocalypse Element)
The Morestran Orthodox Church is based on Archetryx. (PDA: Zeta Major)