If it were truly sunset Saturday to sunset Sunday, then a 10pm Mass on Sunday evening wouldn’t fulfill our Sunday obligation. But it does – so what you are saying is flat-out untrue. (Unless you have a source? …)
FYI, if you’re ever near a college town they tend to have these late-night Masses. I myself recall dragging my feet when I attended good ol’ U of Michigan.
Something that might help, from another thread on the forums:
Most of the Church’s liturgical days run concurrently with the calendar day, i.e. midnight to midnight. There a three exceptions:
Sundays - includes the whole calendar Sunday and the previous calendar Saturday evening;
Solemnities - includes the whole calendar day on which the solemnity falls and the previous calendar day’s evening; and
Feasts of the Lord in the General Roman Calendar that fall on Sundays in Christmas or Ordinary Time - includes the whole calendar Sunday and the previous calendar Saturday evening.
Therefore, calendar Saturday evenings are liturgically part of Sunday and if Mass is celebrated on Saturday evening it is the Sunday Mass and it fulfils the obligation.
Any Mass celebrated at any time on the calendar Sunday is the Sunday Mass and it fulfils the obligation.
Further comments on this can be found at: