The December 25 date is actually the Christians appropriating the feast day of another god -- Mithras (they did this for most of the feast days of saints.) According to many, many scholars the evidence in the book says spring... "shepherds watching their flocks by night."

Shepherds don't have their flocks out in the fields in winter (they're penned up.) They take them out in the spring so they can eat the new grass.

Nor is the evidence for 0 AD or 1 AD very good. There's some serious timeline problems with the Herods in the Bible, indicating a confusion of Herod Antipater and Herod the Great (basically overlapping a lot of details of the different rulers) and so on and so forth. And some of the things never happened ("slaughter of the children") -- such a thing would have been commemorated by the Jews and would have made its way into Jewish religious literature. It most certainly would have started riots and a full-scale rebellion of the province.

-- Byrd
Moderator, Hall of Ma'at