Now when the even was come, he {h} sat down with the twelve.

(h) Because the Law appointed them to be wearing footwear, and to have their staffs in their hands, as though they were is haste, therefore it is to be gathered that they did not sit down when they ate the Passover, but stood, for normally when they went to eat they took off their shoes: therefore he speaks here in this place, not of the Passover, but of the supper which was celebrated after the Passover was solemnly done.

People's New Testament

26:20 When the even was come. The lamb was slain between two evenings, that is, between three and five o'clock (see the margin of Ex 12:6 in the Revised Version). The supper followed on the same night. It was probably dark before the Savior and the twelve came to the guest chamber. The band that sat down to this supper and this occasion have furnished the subject of one of the greatest paintings ever created.

Wesley's Notes

26:20 Mark 14:17; Luke 22:14.

Scofield Reference Notes

[2] sat down with the twelve

The order of events on the night of the Passover supper appears to have been:

(1) The taking by our Lord and the disciples of their places at the table;

(2) the contention who should be greatest;

(3) the feet washing;

(4) the identification Judas as the traitor;

(5) the withdrawal of Judas;

(6) the institution of the supper;

(7) the words of Jesus while still in the room Mt 26:26-29 Lk 22:35-38 Jn 13:3-35 Mt 14:1-31

(8) the words of Jesus between the room and the garden Mt 26:31-35 Mk 14:26-31 Jn 15:16,17 it seems probable that the high-priestly prayer Jn 17:1-26 was uttered after they reached the garden;

(9) the agony in the garden;

(10) the betrayal and arrest;

(11) Jesus before Caiaphas; Peter's denial.

Matthew Henry's Concise Commentary

26:17-25 Observe, the place for their eating the passover was pointed out by Christ to the disciples. He knows those hidden ones who favour his cause, and will graciously visit all who are willing to receive him. The disciples did as Jesus had appointed. Those who would have Christ's presence in the gospel passover, must do what he says. It well becomes the disciples of Christ always to be jealous over themselves, especially in trying times. We know not how strongly we may be tempted, nor how far God may leave us to ourselves, therefore we have reason not to be high-minded, but to fear. Heart-searching examination and fervent prayer are especially proper before the Lord's supper, that, as Christ our Passover is now sacrificed for us, we may keep this feast, renewing our repentance, our faith in his blood, and surrendering ourselves to his service.