It happened, when all the kings of the Amorites, who were beyond the Jordan westward, and all the kings of the Canaanites, who were by the sea, heard how that Yahweh had dried up the waters of the Jordan from before the children of Israel, until we were passed over, that their heart melted, neither was there spirit in them any more, because of the children of Israel.
So this is the first Passover in the Promised Land. They came in just four days beforehand, circumcised themselves, and now are beginning this new relationship with God observing the Passover now in the new land.