Remember, you can check the full document, Paschale Solemnitatis, on this site, among many on the internet. The Triduum begins with Mass on Thursday night:
44. With the celebration of Mass on the evening of Holy Thursday “the Church begins the Easter Triduum, and recalls the Last Supper, in which the Lord Jesus, on the night he was betrayed, loving unto the end his own who were in the world, he offered to the Father his Body and Blood under the species of bread and wine and gave them to the Apostles as spiritual nourishment, and he commanded them and their successors in the priesthood to perpetuate this offering”. (Cf. Ceremonial of Bishops, 297)
With respect to the description cited in the Ceremonial of Bishops, most Gospel accounts relate “disciples” at the Last Supper, not apostles alone.
A suggestion for preachers:
45. Careful attention should be given to the mysteries which are commemorated in this Mass: the institution of the Eucharist, the institution of the priesthood, and Christ’s command of (familial) love; the homily should explain these points.
A word about the time for the Mass, as well as participation of more than one priest:
46. The Mass of the Lord’s Supper is celebrated in the evening, at a time that is more convenient for the full participation of the whole local community. All priests may concelebrate, even if on this day they have already concelebrated the Chrism Mass or if, for the good of the faithful, they must celebrate another Mass. (Roman Missal, Evening Mass of the Lord’s Supper)
Early evening seems to be nearly universal for the starting time for the Holy Thursday Mass. Rome provides for a second Mass, or for this Mass to be celebrated in the morning, but I can’t ever recall an instance where I’ve heard of this actually taking place:
47. Where pastoral considerations require it, the local ordinary may permit another Mass to be celebrated in churches and oratories in the evening, and in the case of true necessity, even in the morning, but only for those faithful who cannot otherwise participate in the evening Mass. Care should nevertheless be taken to ensure that celebrations of this kind do not take place for the benefit of private persons or of small groups, and that they are not to the detriment of the main Mass.
And no private Masses:
According to the ancient tradition of the Church all Masses without the participation of the people are forbidden on this day. (Roman Missal, Evening Mass of the Lord’s Supper)
Not sure how much there is to discuss. Ever hear a great homily on Holy Thursday? Did it cover one or more of the points in PS 45? What about that second Holy Thursday Mass? Anyone with experience of that?