It makes sense that if zecheriah was the high priest we know the day of his vision would be on the day of atonement.
This article shows this is accepted in tradition. And leads to the understanding Christmas to be on 25 december
We really can celebrate christmas as a holy day.
A true day of rejoyce in the birth of Jezus.
Arguments against zechariah being the high priest that year may be valid, but do not exclude the possibilty of zechariah beeing present around the day of atonement. If he was not high priest that year his order could have served in the week before the day of atonement, during the following feast of tabernacles all priests would have been present and so Zechariah would have returned home after that still making the date in december likely.
This link is an interesting article about that
When Was Jesus Born? Zechariah’s Priestly Service