In a Wed. Night Passover meal/Thursday crucifixion . . . .
John 12:1. Six days before . . . . Jesus leaves Jericho and travels to Bethany to Lazarus’ house, arriving before evening on Friday. Partakes of a Shabbat meal Friday night. Then (Probably on Saturday) It’s noised that Jesus (the man who raises the dead) is at Lazarus’ house (the dead man who was raised) and everybody makes the short trek to Bethany, just outside Jerusalem, to see these men. The priests are used to being the center of attention on this day in particular, because this day is the 10th of Nissan. The day that the Lamb is chosen. Obviously the people choose the Lamb, and the priests also choose the sacrificial lamb. The next day, Sunday is the day that Christ rides in on the donkey and ends up at the House/Temple and proceeds to purge the house of leaven. (A requirement before the lamb is brought into the house for the 4 days of testing). The Lamb is tested Sunday (11th), Monday (12th), Tuesday (13th) and Wednesday (14th), then (the common lamb) killed Wednesday afternoon for the Pascha meal and partaken of in the evening (beginning of the 15th day).
The 15th Day for the non priests was typically was a day to continue the feast from the night before, but also to present their sacrifices for the sin offering, the trespass/peace offering and their burnt offering. (See Leviticus 1-7) It was also the day of Firstfruits that were to be offered to the priests. Specifically, barley, liquors and wine, and the firstborn of beasts and substitute offerings for the firstborn of man. (Ex 22:29, 34:20, Num 3, 8:17,18) These “firstfruits” belonged by right to the Levites because they were substituted for the firstborn (Numbers 3) and it was literally a Priests only Passover feast. (The common man had to wait to celebrate his Firstfruits feast til Pentecost). This is the specific Passover Feast that John 18:28 is referring to.
So with Thursday being the 15th when Christ was crucified, you have the day the lamb was to be chosen, then 4 days for testing, Christ observing the common Passover meal on the correct day (and apparently following it with a Lords Supper/Communion per Johns account) followed by his betrayal in the garden, rejection by the (priestly?) Jews before Pilate 6am, followed by the Crucifixion 9am, darkness at noon and death by 3pm. About 6 pm (which was the beginning of the following day, Friday) Matt 27:57, Mark 15:42 Now when even was come, because it was the preparation, that is the day before the sabbath” [Saturday] Joseph of Arimathea . . . . Went in boldly unto Pilate and craved the body of Jesus”.
So Joseph begs the body of Jesus on Thursday evening after 6pm making it the beginning of Friday, the 16th. He burys the body Thursday eve/night, the women buy the spices etc and begin doing whatever they did to process them. Unfortunately they do not finish the process by the time that the sabbath starts the following evening on the 17th, and so they have to wait to anoint the body till after the sabbath is completed, which they do early in the morning on the 18th.
You also have the account in Matthew 27:62 where the day after the preparation (not of the sabbath) the chief priests and Pharisees came together unto Pilate and requested a guard. I’m having a hard time believing that they would seek an audience with Pilate on the sabbath, though apparently they brought a man to trial on the Passover night, so ?
Nisan 15 was the day of preparation specifically because Moses instructed them to be ready to be thrust out Ex 11:1, and yet in Ex 12:39 . . . Because they were thrust out of Egypt, and could not tarry, neither had they prepared . . . 41) And it came to pass at the end of the four hundred and thirty years, even the selfsame day it came to pass, that all the hosts of the Lord went out from the land of Egypt. It is a night to be much observed unto the Lord for bringing them out of the land of Egypt: this is that night of the Lord to be observed of all the children of Israel in their generations.
The night that they were to prepare to leave was important, but it was the night that they left that changed the history of the world. The day in between the nights was the day that they scrambled to prepare to leave.