[Buggman]

It's actually possible. The way it worked is that each of the 24 orders, or courses, of priests served for a week, and then the whole priesthood came together to handle the extra inflow of worshipers and sacrifices during the pilgrimage Feasts: Passover, Shavuot (Pentecost), and Sukkot (Booths). The Talmud actually tells us that the order of Aviyah ministered the week before Shavuot, which means that Zachariah would have stayed for two weeks before returning home. Factor in travel time to return to his wife (since John wasn't virgin-born) and you have John conceived in mid-summer.

Of course, since there were only 24 orders, that meant that each served twice a year on opposite ends. So Zachariah would have also served about six weeks after Sukkot before returning, potentially pushing John's birth to early- or mid-winter.

The reason I believe the first option has to do with the significances of the Feasts. It makes far more sense for John to have been born at Passover (when expectations for the coming of Elijah are at their highest) and Yeshua on Sukkot (when we celebrate the building of the Tabernacle and Temple and God dwelling with His people) than the other way around.

Shalom!

[Tolkien]

That was it. It was the twice a year thing.

I'm just joyful that Jesus came to save my life. Hallelujah.