'On that Day' in the Bible

Then the priest will offer one for a purification offering and the other as a burnt offering, and make atonement for him, because of his transgression in regard to the corpse. So he must reconsecrate his head on that day.

It happened that some men who were ceremonially defiled by the dead body of a man could not keep the Passover on that day, so they came before Moses and before Aaron on that day.