Matthew 12:40 - "For as Yonan was in the belly of the fish three days and three nights, likewise will the Son of man be in the heart of the earth three days and three nights."
We know that it was about 6:00 p.m. (just before sunset) by the time Y'shua's body was put in the tomb. Considering that this was on the day of Pesach and the next day was the High Day (Shabbat) of Feast of Unleavened Bread (FULB), they were racing against time (setting of the sun) so as not to break the Shabbat. Because Y'shua's body went into the tomb just before the setting of the sun we do not include the day of his sufferings as one "day" in the tomb, as it was only minutes before sunset that his body was put into the tomb.
If the period of three days and three nights were to be truncated into shorter time frames, naysayers might have suggested he was still alive when his disciples took him off the torture stake, even though he had been pierced and blood and water came out of his side - but maybe he was faking it? Rather than leave any shadow of a doubt, Y'shua stated that he would be in the heart of the earth "three days and three nights"; after this length of time a corpse is about as dead as it's ever going to get.
The tomb was located just outside the city walls. Historians suggest it was perhaps a 10 or 15 minutes' walk from the city (John 19:42). "Now on the first day of the week, at dawn while still dark, they came to the tomb and brought the spices, those, which they had prepared". (Luke 24:1). John also confirms with Luke that it was dark when they went to the tomb, "On the first of the week, in the morning while it was dark, Maryam of Magdala came to the tomb and saw that the stone was removed from the grave." (Yochanan 20:1).
John was also an eyewitness, whereas Matthew, Mark and Luke are writing from second hand information. As we read all four accounts it is clear that there were several trips made to the tomb by various disciples (Luke 24:22-24), but even in those very early morning visits while it was dark, the tomb was already empty. Matthew says, "Now in the closing (evening) of the Sabbath, as the first of the week was dawning, came Maryam of Magdala and the other Maryam that they might see the grave" (Matthew 28:1). They would certainly wait for Shabbat to end before returning to the tomb but they were also very anxious to see what was going to happen next; they all knew that Mashiyach said three days and three nights, so we can be sure that they were marking off the time.
Why didn't they go to the tomb on Friday if it wasn't a high day? Perhaps some of the disciples did stroll over on Friday, but Pilate had set guards at the tomb for three days (Matthew 27:64), and there wasn't any news to report on Friday. There are ten references in the Good News of Y'shua being in the tomb for three days. When His disciples met Him on the Road to Emmaus later that Sunday afternoon they said, "...And behold, three days have passed since all these things happened." (Luke 24:21).
Three days is an important prophetic duration of time concerning Mashiyach ben Yoseph; "The three branches are three days: Yet within three days shall Pharaoh lift up your head, and restore you unto your place: and you shall deliver Pharaoh's cup into his hand." (B'resheet/Genesis 40:12, 13). Generally when the term "three days" is mentioned, it means three days as in a person worked for three days and got paid three days wages.
It was a "three day" journey for the Israelites from the slavery of Egypt to the freedom to worship YHWH (Sh'mot/Exodus 3:18). It was three days of preparation and readiness for Israel to cross over the Jordan and enter into the promised land (Joshua 1:11). Anyone who touched a dead body was considered unclean for seven days, but they purified themselves on the third day and on the seventh day where considered clean (B'midbar/Numbers 19:12).
Shabbat is the pinnacle of the week, as Shabbat ends we “descend” toward Sunday, Monday and Tuesday, but then Wednesday we begin to ascend up to Thursday, up to Friday and then reach Shabbat as the highpoint of the week. All who observe Shabbat know Shabbat to be the most cherished day of the week. The Seventh Day Shabbat is a complete and perfect day where YHWH's people abide in His Word enter into His Rest and learn from the Ruach haKodesh. Wednesday is the first of three days that make aliyah (go up) towards Shabbat. Mashiyach's resurrection on the Seventh Day also symbolizes the seventh Millennium when he will come again to rule and reign. Therefore it is consistent that Y'shua would resurrect on Shabbat as the day of unity.
When we choose to believe that Y'shua meant "three days and three nights" as a literal span of time, then we also must conclude that he was put in the tomb late on Wednesday. From this point we count Wednesday night and Thursday as one complete day, Thursday night and Friday as two complete days, Friday night and Shabbat as three complete days and nights. This also means that Y'shua rose from the tomb on Shabbat whereas a Thursday crucifixion would either be missing half a day or having him rise on Sunday afternoon, which doesn't work. It was the Christian world that introduced things like "inclusive reckoning" and the theology that Mashiyach rose with the sun on Sunday morning as the "sun of righteousness".
(This makes about as much sense as insisting that our Savior was born on the 25th of December when the Bible clearly tells us He was born on the first day of Sukkot/Tabernacles, which is a FALL festival!) Most Christians attend church meetings on Sunday in commemoration of a Sunday sunrise resurrection which is sheer paganism. In Y'shua's days sun worship was the religion of the majority; it was the majority religion of most Greeks who became Christians which is why Sunday services were installed in opposition to the Seventh Day Shabbat. The Seventh Day Shabbat was given at the Creation of the world as a sign between YHWH and His people, whereas Sunday is a counterfeit "Sabbath".
The idea of a Sunday sunrise resurrection connects back to Ezekiel 8:16 - "And he brought me into the inner court of YHWH's house, and, behold, at the door of the temple of YHWH, between the porch and the altar, were about five and twenty men, with their backs toward the temple of YHWH, and their faces toward the east; and they worshipped the sun toward the east." Most Christians are turning their backs on Shabbat and Torah and the Word of YHWH because they follow a religion that tells them that "Jesus (or Paul) did away with the law".
But YHWH says that He gave Torah so that His people would not turn to these things, "And lest you lift up your eyes unto heaven, and when you see the sun and the moon and the stars, even all the host of heaven, should you be driven to worship them and serve them, which YHWH Elohim has divided unto all nations under the whole heaven." D'varim/Deut. 4:19.
Most Christians think it is acceptable to "sanctify" Sunday "in the name of Jesus" and many wouldn't think to bow before the sun and worship it; but nevertheless, they pay homage to institutions that have changed "times and laws" (Daniel 7:25) so whether Christians realize it or not, Sunday worship was ripped right out of paganism and has nothing to do with what Yeshua Himself practiced and taught.