'First Day' in the Bible

From the first day of the seventh month began they to offer burnt offerings to Yahweh: but the foundation of the temple of Yahweh was not yet laid.

The children of the captivity did so. Ezra the priest, [with] certain heads of fathers' [houses], after their fathers' houses, and all of them by their names, were set apart; and they sat down in the first day of the tenth month to examine the matter.

They made an end with all the men who had married foreign women by the first day of the first month.