Three days and three nights

Jesus clearly said He would be in the heart of the Earth for 3 days and 3 nights. Matthew 12:40.

During that time He preached to the Spirits in Hell or prison. He did this so that all before and after His 1st advent on Earth would have the opportunity of following Him. 1 Peter 3:18-19.

He had His symbolic meal, establishing the New Covenant on the 14th of the first month (Abib or Nisan). The meal happened after sunset which is the start of the 14th day.

He prayed, was betrayed, arrested, tried, was beaten, crucified and buried all on the 14th which was Biblically (old testemant) the Passover and preperation day.

At sunset began the 15th; in Jesus' time as is today traditionally called Passover or Unleavend bread, but Biblically Passover was the previous day.
After Babylonian captivity Jews combined the two days and the gospels record as such. Any Jewish calender too confirms that the Jews in Jesus day and today have Passover on the 15th. Exodus 12 confirms the 14th.

At sunset the 15th Jesus was already buried. This was a Sabbath or Holy day but not the 7th day Sabbath. It was a Wednesday night, Thursday day. It was biblically the 1st of Unleavened bread, traditionally then as now Passover as well.

Jesus was in the grave Wednesday, Thursday and Friday nights; and Thursday, Friday, Saturday days. Some time on the first day beginning Saturday night at sundown and before dawn on Sunday morning (all the 1st day) Jesus was resurrected. When Mary arrived at sunrise He was already up.

Those 3 days and nights Jesus preached as Peter records to those in the grave. What their condition was or how He did what He did GOD knows, but it is what Holy Spirit records and what was done.

Jesus had to be in the grave 3 days and 3 nights in order to fulfill Scriptural and His own prophecy.