What time can Midnight Mass begin?
The following day is, of course, the feast of the Nativity of our Lord, the first day of Christmas, on 25 December. A popular question in novus ordo circles is: What time does Midnight Mass begin? The novus ordo is not our concern, but if the question is about the traditional Latin Mass, the answer is clear: no earlier than midnight on 25 December. There is no permission to use the next calendar day's propers for the traditional Latin Mass on the evening before a Sunday or holy day, even at 11 p.m.
4. Dies liturgicus est dies sanctificatus actionibus liturgicis, praesertim Sacrificio eucharistico et publica Ecclesiae prece, id est Officio divino; et decurrit a media nocte ad mediam noctem.
4. The liturgical day is the day sanctified by the liturgical rites, especially the eucharistic Sacrifice and the public prayer of the Church, that is the divine Office; it runs from midnight to midnight.
Based on the 1962 rubrics, Midnight Mass (Christmas Mass During the Night) must begin at midnight. A 10 p.m. or 11 p.m. Mass on 24 December, while technically fulfilling one's 25 December obligation, must use the violet vestment Mass of the Vigil of the Nativity of our Lord, the same Mass propers used earlier that morning.
28. Furthermore, by virtue of its character of special law, within its own area, the Motu Proprio Summorum Pontificum derogates from those provisions of law, connected with the sacred Rites, promulgated from 1962 onwards and incompatible with the rubrics of the liturgical books in effect in 1962.