They are having a service Saturday night. In New Testament times, the day went from sunset to sunset. So they are still meeting "on the first day of the week" as required.
If this were any other day but Christmas, no one would care. But many have turned a pagan holiday and man-made tradition into a biblical command.
REQUIRED????
The value I observe has nothing to do with a Biblical command. Rather, a regularly scheduled day of worship is now sitting second seat to a man made holiday that ironically was developed to glorify Christ, but is now used as a reason to place a family gettogether prior to the worship of Christ.