Read Exodus 12. Tenth of the month, lamb selection is Palm Sunday. Passover, Crucifixion was on the fourteenth. Check a calendar, try May. If the tenth is a Sunday then the fourteenth is a Thursday.

When the gentile believers decided on passion week traditions, they didn’t study the Torah but just the gospels.

Read Leviticus 23.
Just like Christmas is a day but also a season. Passover and unleavened bread get blurred in the vernacular.
In Lev 23 we see Passover, the next day starts the seven days of unleavened bread
  The first day is a day of no work, an annual feast Sabbath. During the seven days would be a weekly Sabbath. The day after, during the seven day feast, would be the feast of first fruits.

Now a biblical day starts at sundown, not midnight like our current calendar. See genesis 1 six times evening and morning is a day. Also Exodus 12 18 Leviticus 23 32 and Psalm 55

Wed night that year, translating to our calendar, was the last supper – a gallilean tradition worth researching. Thursday at 3 pm Messiah died just at the time of the Passover lamb
See John 19:31. Preparation day for an especially important Sabbath. Prep day is the day before. Luke 23:54 more general “a Sabbath”.
The men place Jesus in the tomb, the women go home and prepare spices (not realizing the men had them). They rested for 2 Sabbaths. Matthew 28 1 when literally translated says Sabbaths. This was translated out, people assumed it was a copy error.
Mark 16:1. Sat night after the Sabbath ( ends at sundown). The women go buy more spices. Verse 2 in the morning go to the tomb

Mark 16:9. Early on the first day, ie Sat night, He arose.

Thursday afternoon, 5th day Crucifixion to Sat night First day Resurrection.
3 days and 3 NIGHTS in the grave. 5th day, 6th night and day, 7th night and day, 1st night

He also arose on the third day (of unleavened bread).
He arose on first fruits. See 1 Corinthians 15
https://icogsfg.org/jc-wavsh.html

It wasn’t about the day of the week but the 3 spring feasts of Leviticus 23. Pentecost fulfills Shavuot. The 3 fall feasts foreshadow the second coming.

Early first century believers kept Sabbath Acts 15 21 then met Sat night to honor the resurrection Acts 20:7.