'First Day' in the Bible

And the LORD spoke unto Moses in the wilderness of Sinai, in the tabernacle of meeting, on the first day of the second month, in the second year after they were come out of the land of Egypt, saying,

And they assembled all the congregation together on the first day of the second month, and they declared their ancestry by their families, by the house of their fathers, according to the number of the names, from twenty years old and upward, individually.

And he that offered his offering the first day was Nahshon the son of Amminadab, of the tribe of Judah:

On the first day shall be a holy convocation; you shall do no manner of regular work on it:

And in the seventh month, on the first day of the month, you shall have a holy convocation; you shall do no regular work: it is unto you a day of blowing the trumpets.

And Aaron the priest went up into mount Hor at the commandment of the LORD, and died there, in the fortieth year after the children of Israel were come out of the land of Egypt, in the first day of the fifth month.