What follows is a very brief outline of a chapter in a book by Joachim Jeremias. I find his argument very convincing and I can no longer see any reason for casting doubt on the Synoptics’ timing. Jeremias shows that John, too, was describing a Passover *seder, *despite what he says about the priests’ reasons for not entering the palace (Jn 18:28). In at least five other places John describes what can only be a Passover meal:
**1. An evening meal beginning after dark.―**This was something that happened only on special occasions, such as a wedding or a circumcision, and also the Passover seder, as laid down in Tractate Zebahim (Sacrifices) 5:8.
John 13:30, and it was night.
Mk 14:17, Mt 26:20, When evening came, …
1 Cor. 11:23, On the night he was betrayed, …
**2. They were reclining, not sitting.―**Also only on special occasions, including the Passover seder. Tractate Berakot (Benedictions), five references.
John 13:23, One of them, the disciple whom Jesus loved, was reclining next to him … Leaning back against Jesus, he asked him, …
Mk 14:18, While they were reclining at the table, …
Mt 26:20, Jesus was reclining at the table with the Twelve.
**3. All were ritually clean. **
John 13:10, Jesus answered, “A person who has had a bath needs only to wash his feet.”
**4. “What you are about to do, do quickly” (John 13:27-29).―**Some of the Twelve thought Jesus was telling him to buy what was needed for the feast, or to give something to the poor. Nobody asked Jesus what Judas was going out to do. “Quickly” could mean “before the stores shut.” If it was 13 Nisan, there would be no such hurry.
**5. Jesus does not return to spend the night at Bethany.―**The night of Passover had to be spent within the Jerusalem city limits, which included the western slope of the Mount of Olives.
John 18:1, Jesus left with his disciples and crossed the Kidron Valley [to] an olive grove.
Mk 14:26, Mt 26:3409, They went out to the Mount of Olives.
Lk 22:39, Jesus went out as usual to the Mount of Olives and his disciples followed him.
Source: Joachim Jeremias, *The Eucharistic Words of Jesus, *pp. 44-55. Jeremias lists several further arguments, all pointing in the same direction. I have picked out the five I find most convincing.