When did the Lord's Supper be set? (Mt 26:29; Lk 22:15-18)

below is by  Dan Jenkins at https://churchofchristarticles.com/kingdom-lords-supper/

Jesus taught the Lord’s Supper would be part of the kingdom. It was in the upper room that Jesus promised He would eat the Lord’s Supper with His followers when the kingdom came. Jesus said, “But I say to you, I will not drink of this fruit of the vine from now on until that day when I drink it new with you in My Father’s kingdom” (Matt. 26:29). He and eighty-three other Divinely sent messengers had proclaimed that the kingdom was about to be established. 

Now in the upper room, what Jesus said placed a time limit on the time it would come. He said, “With fervent desire I have desired to eat this Passover with you before I suffer. For I say to you I will no longer eat of it until it is fulfilled in the kingdom of God . . .  I will not drink of the fruit of the vine until the kingdom of God comes” (Luke 22:15-18). His words clearly state that the cup with the fruit of the vine as part of that feast was ending and was about to be fulfilled when Jesus would assemble with the disciples at His table, His supper—the Lord’s supper. The Passover, as a God-appointed feast, was within a year of coming to an end.

below is by Albert Barnes 

Mat 26:18 And he said, Go into the city to such a man, and say unto him, The Master saith, My time is at hand; I will keep the passover at thy house with my disciples.

Go into the city to such a man - That is, Jerusalem, called the city by way of eminence.

Luke says that the disciples whom he sent were Peter and John. The man to whom they were to go he did not mention by name, but he told them that when they came into the city, a man would meet them bearing a pitcher of water. See Mark and Luke. Him they were to follow, and in the house which he entered they would find a room prepared. The name of the man was not mentioned. The “house” in which they were to keep the Passover was not mentioned. 

The reason of this probably was, that Christ was desirous of concealing from “Judas” the place where they would keep the Passover. He was acquainted with the design of Judas to betray him. He knew that if Judas was acquainted with the place “beforehand,” he could easily give information to the chief priests, and it would give them a favorable opportunity to surprise them, and apprehend “him” without making a tumult. Though it was certain that he would not be delivered up before the time appointed by the Father, yet it was proper “to use the means” to prevent it. There can be little doubt that Jesus was acquainted with this man, and that he was a disciple. The direction which he gave his disciples most clearly proves that he was omniscient. Amid so great a multitude going at that time into the city, it was impossible to know that “a particular man would be met” - a man bearing a pitcher of water - unless Jesus had all knowledge, and was therefore divine.