It happened, when Joshua was by Jericho, that he lifted up his eyes and looked, and, behold, there stood a man over against him with his sword drawn in his hand: and Joshua went to him, and said to him, Are you for us, or for our adversaries?
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.