He fell asleep on the late afternoon/evening of the day they reached the Amalienborg palace, slept that night (being asleep when Leaftroll attacked)and the following day (which was the day Mikkel went to Kastellet). He was still asleep when the ghosts hit them, some 24 hours after they arrived. He slept through that, though he was conscious, and in human form, in the dreamworld when the ghosts tried to get into his haven, and had enough connection to his body to grab Emil. Then he slept through their escape from Copenhagen, and woke around mid-morning of the next day. So yeah, likely a bit over thirtysix hours.