'Sixth' in the Bible

In the second year of Darius the king [of Persia], on the first day of the sixth month (Aug 29, 520 b.c.), the word of the Lord came by Haggai the prophet to Zerubbabel the son of Shealtiel, governor of Judah, and to Joshua the son of Jehozadak, the high priest, saying,

on the twenty-fourth day of the sixth month (Sept 21, 520 b.c.) in the second year of Darius the king.