'First Day' in the Bible

And Jehovah spoke to Moses in the wilderness of Sinai, in the tabernacle of the congregation, on the first day of the second month, in the second year after they had come out of the land of Egypt, saying,

And they gathered all the congregation on the first day of the second month. And they declared their pedigrees according to their families, by their fathers' house, according to the number of the names, from twenty years old and upward, by their heads.

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

In the first day shall be a holy convocation. You shall do no kind of laboring work.