During the night of the Passover, Yahweh sends his Destroyer out over Egypt to kill all the firstborns. The Israelites themselves are protected by the apotropaic blood rite of the Passover (#109-110): the lamb’s blood smeared on the doorposts of all the Israelites’ houses ward off the evil of the Destroyer. Thus they are commanded not to leave their houses “until morning”—lest Yahweh’s Destroyer strike them down too!
Yet later in the narrative (Ex 12:31-34) they do indeed leave their houses. First, Pharaoh cries with terror during the evening and beckons Moses and Aaron to come. And then we are informed that all of the children of Israel immediately depart, supposedly during the evening! Or is it?