This year, the fourth Sunday of Advent and Christmas are both days of obligation. There are two distinct obligations. There is an obligation to attend Mass for the Sunday, which can be fulfilled either Saturday evening after 4 p.m. or Sunday during the day before 4 p.m. The obligation to attend Mass for Christmas can be fulfilled either Christmas Eve after 4 p.m. (Sunday evening) or on Christmas day at any time. One must go to Mass twice — meaning, you could go to Sunday Mass in the morning and Christmas Eve Mass later that same day.
You have a few options for fulfilling both obligations for the fourth Sunday of Advent and Christmas:
– Saturday evening, Sunday evening
– Saturday evening, Monday morning
– Sunday daytime, Sunday evening
– Sunday daytime, Monday daytime
Going to Mass once either Sunday morning or evening to cover both obligations. (It doesn’t count!)