Taken from Bart Ehrman’s THE NEW TESTAMENT: A HISTORICAL INTRODUCTION
TO THE EARLY CHRISTIAN WRITINGS, page 47-48:
This now takes us to the dating of Jesus’ execution. The Gospel of Mark, probably our earliest account, clearly indicates when Jesus was put on trial. On the preceding day, according to Mark 14:12, the disciples ask Jesus where he would have them “prepare” the Passover. This is said to happen on the day when the priests “sacrifice the Passover lamb,” or the day of Preparation for the Passover (the afternoon before the Passover meal). Jesus gives them their instructions and they make the preparations. That evening the start of the next day for them they celebrate the meal together (14:17-25).
At this special occasion ,Jesus takes the symbolic foods of the mean and endows with additional symbolic meaning, saying “This is my body…this is my blood of the covenant” (14:22-24). Afterwards , he goes with his disciples to the Garden of Gethsemane, where he is betrayed by Judas Iscariot and arrested (14:32, 43). He is immediately put on trial before the Jewish Council, the Sanhedrin (14:53). He spends the night in jail; early in the morning the Sanhedrin delivers him over to Pilate (15:1). After a short trial, Pilate condemns him to death. He is led off to be crucified, and is nailed to the cross at 9:00 am (15:25). Thus in the Gospel of Mark, Jesus is executed the day after the Preparation of the Passover, that is, on the morning after the Passover meal has been eaten
Our latest canonical account of this event is in the Gospel of John: the same persons are involved and many of the same stories are told. There are differences, though, and some of these are significant. John’s account of the trial before Pilate, for example, is much more elaborate (18:29-19:16). In part, this is because in his version the Jewish leaders refuse to enter Pilate’s place of residence and send Jesus in to face Pilate alone. As a result Pilate has to conduct the trial by going back and forth between the prosecution and the defendant, engaging in relatively length conversation with both before pronouncing his verdict. What is particular striking, and significant for our investigation here, is that we are told exactly when the trial comes to an end with Pilate’s verdict : “Now it was the day of Preparation for the Passover, and it was 12:00 noon” (John 19:14). Jesus is immediately sent off to be crucified (19:16).
The day of the Preparation for the Passover? This is the day before the Passover meal was eaten, the day the priests began to sacrifice the lambs at noon. How could this be? In Mark, Jesus had his disciples prepare the Passover on that day, and then he ate the meal with them in the evening after it became dark, only to be arrested afterwards.
If you read John’s account carefully, you will notice other indications that Jesus is said to be executed on a different day than he is in Mark. John 18:28, for example gives the reason that the Jewish leaders refuse to enter intro Pilate’s place of residence for Jesus’s trial. It is because they do not want to be ritually defiled, and thereby prevented from eating the Passover meal that evening (recall, in Mark , they would have eaten the meal the evening before the trial). This difference in dating explains another interesting feature of John’s Gospel. In this account Jesus never instructs his disciples to prepare for the Passover, and he evidently does not eat a Passover meal during his last evening with them (he does not, for example, take the symbolic foods, and say, “This is my body” and “This is my blood”.) The reason for these differences should now be clear: in John’s Gospel, Jesus was already in his tomb by the time of this meal.
We seem to be left with a difference that is difficult to reconcile. Both Mark and John indicate the day and hour of Jesus’s death, but they disagree. In John’s account he is executed on the day on which preparations were bring made to eat the Passover meal, sometimes after noon. In Mark’s account he is killed the following day, the morning after the Passover meal had been eaten, sometime around 9:00 am. If we grant that there is a difference, how do we explain it?