The St. Andrew Christmas novena is traditionally recited 15 times per day starting on November 30th and going through Christmas Day on December 25th.
Since this novena is prayed during Advent, it perfectly helps us to prepare our hearts for the coming of Christ as Christmas, one of the main purposes of the Advent season.
One tip with this novena: if you have scrupulosity trying to pray the novena exactly 15 times per day, simply pray it every time it comes into your mind during each day.
Hail and blessed be the hour and moment In which the Son of God was born Of the most pure Virgin Mary, at midnight, in Bethlehem, in the piercing cold. In that hour vouchsafe, I beseech Thee, O my God, to hear my prayer and grant my desires, (here mention your request), through the merits of Our Saviour Jesus Christ, and of His blessed Mother. Amen.