Section — Prümmer, Manuale Theologiae Moralis
§ 3. On the Hour at Which Mass Is to Be Celebrated
290. By common law, the celebration of Mass can begin from one hour before dawn until one hour after noon.456
By dawn is understood here twilight, which customarily arrives about two hours before sunrise. All theologians say that this time is to be taken morally and not mathematically, so that he who says Mass a little before or after it has no fault. Dawn varies greatly according to different times and places. In central Europe during the month of June dawn begins almost at midnight. Therefore, according to strict law, Mass can be said then even from midnight; yet it is unbecoming for this to be done without a grave cause. In polar regions, however, where dawn does not appear on some days, the Sacred Congregation of Rites granted on September 18, 1634, that Mass could begin from the beginning of civil life, that is, at the time when men customarily rise in the morning for their labors according to the approved customs of the regions.
The precept not to celebrate outside the hours established by the rubric binds of itself under grave sin; accordingly, he who without any legitimate cause anticipates or postpones the time considerably, that is, by one hour, sins gravely.457 The reasons for which it is lawful to say Mass earlier or later are the following:
a) The necessity of confecting the Eucharist for administering Viaticum. This is evident of itself; for if it is lawful for this reason to repeat Mass or to say it while not fasting, a fortiori it is lawful to pass beyond the time of celebration.
b) On the night of the Nativity of the Lord, as was said above.
c) A reasonable custom approved by the Ordinary. Thus, for example, it is lawful to say Mass very early in the morning in order that servants and workmen may be furnished an opportunity of hearing Mass.
d) A dispensation given by the bishop or regular superior for a reasonable cause.458 Thus, for example, because of a journey to be made or already made, it is lawful to say Mass before dawn or after noon.
e) A privilege granted by the Holy See. Certain religious possess such a privilege. Pius VI459 granted to the Congregation of Purity that Mass could be said two hours before dawn and two hours after noon. Génicot460 teaches that this privilege is shared by other religious. Indeed, Redemptorists can celebrate Mass in their churches two hours after midnight and three hours after noon.461
456 Code of Canon Law, c. 821, § 1.
457 Cf. St. Alphonsus, Theol. mor. l. 6, n. 346.
458 Cf. ibid., n. 344.
459 January 24, 1783, and May 10, 1785.
460 Theol. mor. II, n. 237.
461 Cf. Marc, Inst. mor. II, n. 1625.
291. Scholion 1. On reciting Matins before Mass. Since the rubric of the Missal says: "The priest ... who is to celebrate Mass ... at least after Matins with Lauds have been completed, etc.," several older authors, for example, St. Antoninus, Antoine, and Gavantus, thought that there was a grave obligation of reciting Matins and Lauds before Mass. This opinion is indeed certain if there is question of choral recitation before the conventual Mass. For those, however, who recite the Divine Office privately, it is also practically certain that this obligation is not grave but only light, and any moderate cause excuses from it altogether, for example, convenience of study, labor to be completed, etc.462
462 Cf. above, II, n. 373; St. Alphonsus, Theol. mor. l. 6, n. 347 ff.
292. Scholion 2. On the time to be employed for the celebration of Mass. With the time and hour of celebration there is in some measure connected the time itself necessary for celebrating, concerning which St. Alphonsus463 rightly teaches "that a priest who completed Mass in less than a quarter of an hour could with difficulty be excused from mortal sin, even if the Mass were one of the shorter ones or the Mass of St. Mary on Saturday; because in so brief a space he must commit two grave defects: one, grave irreverence toward the sacrament; the other, grave scandal toward the people." Therefore the priest is to take care that he employ at least twenty minutes in the celebration of an ordinary private Mass and not exceed half an hour.
463 Ibid., n. 400.