They all come into play at the same time.
Nevertheless, each one will trigger the Grinding Station, so you can stack all the 12 "untap the Grinding Station" triggers, resolve one, activate the Station, resolve the next one, etc ...
This kind of Combo was used in Mirrodin Block MonoGreen with Beacon of Creation and Blasting Station.
Forgive my stupidity, but each time that I activate it based on its new untap, do I have to sacrifice a different artifact that has not been returned to play thanks to Second Sunrise?
Thanks,
Barry