That was Halloween when the dead can walk amongst the living. They addressed it in so many words. That is the only night the ghosts can leave the house. If you recall, the maid went to visit her mother, Tate went to the beach, and the gay guy went out carousing. Hayden also left the house in the security guy's car that night, but disappeared inexplicably at dawn. They were all seen coming home at dawn the next morning as well.
I totally did not catch that at it was the reason they could leave.