The 9th day of Av corresponds to August 4th.
Since Jehoiarib, the first division, was on priestly duty the first week in August, then seven weeks later would be the course of Abijah.
This would be the last week of September in the Roman calendar, or the second week of the Jewish month of Tishri.
This is an important week, as it began with the Day of Atonement, Yom Kippur — the 10th day of Tishri, and ended with the Feast of Tabernacles, Sukkoth — the 15th day of Tishri.
The Infancy Gospel of James (136 A.D.) agrees that Zacharias was serving in the Temple on the Day of Atonement.