Christmas I found...farther roots then the 3rd and 4th Century. Its origin dates back to 202 C. E!
The Watchtower will say that the Great Apostasy began right after the apostles died, at the very end of the 1st Century or early in the 2nd Century. The belief is, the apostles acted as a restraint against apostasy, and after they were gone apostasy flourished.
So, if Christmas dates back to 202 C.E. they will still say it is the result of apostate Christianity, which had been building for 100 years by that time.
The pyramid connection to 1914 is very interesting.