1. "Christmas" means "Christ's Mass" ie, the Lord's supper.
2. Jesus said he would only give ONE sign that He was the Messiah:
Matthew 12:40
For as Jonas was three days and three nights in the whale's belly; so shall the Son of man be three days and three nights in the heart of the earth.
Where's the third night between Friday afternoon and Sunday morning?
I believe that this use of "Christ's Mass" actually refers to the Mass celebrated on Christmas eve, and to the first full day of Christmas, ie, the Feast of the Nativity.
Sunday morning? Try Saturday night.