'First Day' in the Bible

In the eleventh year, on the first day of the month, the word of the Lord came to me:

In the twenty-seventh year, in the first month, on the first day of the month, the word of the Lord came to me:

In the eleventh year, in the third month, on the first day of the month, the word of the Lord came to me:

"'This is what the sovereign Lord says: In the first month, on the first day of the month, you must take an unblemished young bull and purify the sanctuary.