The Jews used a lunar calendar to determine the exact times of their feast days.
The only year that even comes close to the bible account of the death, burial, and resurrection of Christ is 31 AD. In 31 AD the preparation day (John 19:31 & 42) for the feast of the Passover was on Wednesday. The following day was a special High Sabbath, the first day of Passover (John 19:31 cf Leviticus 23:6 & 7).
The first day of Passover was always a special high Sabbath regardless of what day of the week it fell on (Leviticus 23:6 & 7). The first day of Passover was on 15th day of the month of Nisan (sometimes called Abib) and corresponds to our March-April.
The 15th of Nisan, in 31 AD fell on a Thursday, for the Sabbath that was looming at sundown Wednesday was not the weekly Sabbath, but the special high Sabbath, the first day of Passover.
On Friday the ladies went shopping - to buy the spices for the "embalming" process, rested on the regular Sabbath, Saturday, and got to the grave "as it began to dawn toward the first day of the week" or just before sun up on Sunday, and the tomb was already empty!
Wednesday sundown through Saturday sundown, 3 days and 3 nights in the grave, and arose after sundown on what we call Saturday, but what a Jew would call the first day of the week, or Sunday. Three days and three nights in the tomb (Matthew 12:40).
The Jews calculated the beginning and ending of a day differently, even among themselves.
From the writings of Josephus, the Mishna, and other historic Jewish source literature we learn that the Jews of northern Palestine calculated days from sunrise to sunrise. That, of course, included Galilee where Jesus and the disciples had grown up.
The Pharisees, on the other hand, and those from southern Palestine (Benjamin and Judah), used the sunset to sunset means of determining when a day began.
Now we know from our knowledge of geography that Jerusalem is in the south. This had the practical effect of the people gathered in Jerusalem from
all over Palestine, to celebrate Passover on two adjoining days and also allowing the temple sacrifices to be made over a four hour period rather than just two, and helped to keep the northern people separate from the southern and thus avoiding regional and other types of clashes between the two very different peoples. (Remember the southern Jews disdain for northern Jews, "Can any good thing come out of Galilee?")
So, it is simple to see that Jesus and the disciples considered Passover (the preparation day) to have started at sunrise and to have ended at sunrise the next day! The southern Jews, however, considered the preparation day to begin at sundown. Therefore, by God's Sovereign design, Jesus could celebrate the Passover with the disciples, and still be taken for sacrifice at the very time the southern Jews were sacrificing their lambs.
It is obvious that when He ate the meal with the disciples, it was purposely done early so they could enjoy that one last time of fellowship, the Lord's Supper could be instituted (the Lord's Supper is NOT a Passover Seder, if it were it would only be done ONCE per year, not "as oft as ye do it) Judas could be identified, etc.
