'First Day' in the Bible

The Lord spoke [by special revelation] to Moses in the Wilderness of Sinai in the Tent of Meeting (tabernacle) on the first day of the second month in the second year after the Israelites came out of the land of Egypt, saying,

and assembled all the congregation on the first day of the second month, and they registered by ancestry in their families (clans), by their fathers’ households, according to the number of names from twenty years old and upward, head by head,

Now the one who presented his offering on the first day was Nahshon the son of Amminadab, of the tribe of Judah;

On the first day there shall be a holy [summoned] assembly; you shall do no laborious work that day.

‘On the first day of the seventh month, you shall have a holy [summoned] assembly; you shall do no laborious work. It will be for you a day of blowing the trumpets (the shophar, ram’s horn).

Aaron the priest went up on Mount Hor at the command of the Lord, and died there in the fortieth year after the Israelites came out of the land of Egypt, on the first day of the fifth month.