Sanctuaries reset 14 days after they are activated. Sanctuaries are active as soon as the first creature since the last reset is placed in them. This means that every Sanctuary on the Map can have a different amount of time left before they reset!

When the reset happens, the Sanctuary returns to Level 0 and all creatures within are returned to their owners. All unlocked Slots also return to their locked state; only the first 4 remain unlocked.