This verse is commonly misunderstood in relation to the timing of Christ's death and resurrection. Two of the disciples, traveling to Emmaus, were conversing with the resurrected Christ, though they did not know it was He (verses 13-16). They were rehearsing what had happened in Jerusalem to Jesus by the chief priests and rulers of Judea (verses 18-20).
This conversation occurred on Sunday, the same day that the women, Peter, and John had gone to the tomb only to find it empty. Yet these disciples heading to Emmaus say that it had only been three days, not four. How do we reconcile this to the overwhelming body of evidence that Christ was buried on a Wednesday afternoon and raised again on a Saturday afternoon?
The key is in the repetition of the words "all these things," "these things," and "the things" of verses 14, 18-19 and 21. "Things" is modified by the disciples' specifying in verse 20 that they were speaking of the actions that "the chief priests and our rulers" had done to Christ. The fact that is often forgotten is that their ignominious actions against Him did not end with delivering Him to Pilate for crucifixion! (See Matthew 27:62-66.)
The day after "the Day of Preparation" was Thursday, the first day of Unleavened Bread. These Jewish leaders went to Pilate on the holy day to "guarantee" that their Messiah would not rise from the dead. And with the guard in place and the tomb sealed, they felt certain nothing more would happen.
Thus, when the two disciples on the road to Emmaus say that Sunday "is the third day since these things happened," they are counting from the last despicable actions of the chief priests and Pharisees on Thursday, not Wednesday. Note that their words preclude a Friday crucifixion as well, since Sunday is only the second day from Friday.