Personally, I regularly attend Mass at Sunday 9pm at the College Chapel while at university. It’s the Mass most university student attend (literally standing room only, it’s a joy just to see). Although, I would still call my “regular” Mass time Sunday morning, I just go to the 9pm one because it’s the one me and all my peers go to.
That’s not right.
If this year my parish celebrates a Mass of Christmas at 6 p.m. Christmas Day and I have already participated in any one of the 4 Masses of Christmas (Vigil, Midnight, Dawn or Day), my participation in that 6 p.m. Mass fulfills my obligation for Sunday regardless of the fact that the Mass being celebrated is not the Feast of the Holy Family.
That I know is true. If you have a Holy Day of Obligation, you can fulfill it by attending a Mass or Divine Liturgy in any Rite or Form of the Catholic Church regardless of what they’re actually celebrating (OF, EF, Ukrainian DL).
I saw this in another thread, but here’s what the
Canadian Bishop’s had to say about Christmas on Saturday/Monday:
When Christmas Is Celebrated on Saturday
It is important to keep the celebration of Christmas and Sunday distinct, and to be mindful of the extra demands which are placed upon priests and other liturgical ministers when Christmas and Sunday are celebrated on consecutive days.
The following recommendations will be helpful.
a) If possible, additional celebrations of the Vigil Mass of Christmas are to be avoided.
b) If necessary, only one anticipated Midnight Mass should be celebrated around 10:00 p.m.
c) The regularly scheduled Saturday evening Mass in anticipation of Sunday should be omitted altogether.
When Christmas Is Celebrated on Monday
Sunday is the original and primary feast day for the Christian people, and the heart of the liturgical year. Christmas, the cele bration of the incarnation of the Son of God and of his birth as our Saviour, is a distinct feast. For this reason, the two celebrations should be kept distinct. It is therefore recommended that no Sunday Mass be celebrated on Sunday evening, in order to avoid any confusion between the two celebrations. If possible, additional Vigil Masses for Christmas should be avoided, and if necessary, only one antici pated Midnight Mass should be celebrated around 10:00 p.m.
The CCCB seems to be pretty clear that this year (Christmas on a Saturday), the 2 days are distinct from each other. They even go so far as to recommend that no Masses be celebrated on Saturday evening (which would be Christmas celebrations) so that people don’t conflate the 2 days together.
Canon Law obliges Catholics to attend Mass on Holy Days, and the CCCB says that they are distinct celebrations. The implication is that both carry a separate obligation (and the recommendations state not to put any Masses in the “crossover” time just to be sure).
Personally speaking, Christmas on a Saturday is not really an issue as I’ll be going Friday evening to the Christmas Eve Mass (not the official name, I know. Just fill in whatever name we’ve decided is correct

), and then again Sunday morning as I always do when I’m at home (not at university).
Christmas on a Monday would be much more of a hassle because I’d probably go Sunday morning then again Sunday evening.