This is crucial to understand because many believe that Christ was only dead and buried in the grave for about 36 hours (Friday night to Sunday morning) which denies that He was who He said He was!
A: Exactly 72 hours: from Wednesday just before sunset to Saturday just before sunset.
Jesus did many miracles while on Earth, but he gave only one sign that He was the Messiah.
Matthew 12:38 Then some of the scribes and Pharisees answered, saying, “Teacher, we want to see a sign from You.”
Matthew 12:39 But He answered and said to them, “An evil and adulterous generation seeks after a sign, and no sign will be given to it except the sign of the prophet Jonah.
Matthew 12:40 For as Jonah was three days and three nights in the belly of the great fish, so will the Son of Man be three days and three nights in the heart of the earth.
In other words, Jesus was who He said He was, then He would be dead in the ground for this amount of time or we could not consider Him the Son of God.
When we harmonize the supporting Gospel accounts of this event we find that there is only one length of time that it could be.
John 2:19 …in three days (no more than 72 hours)
Mark 8:31 …after three days (no less than 72 hours)
Matthew 16:21 …the third day (no less than 48 hours and no more than 72 hours)
The only amount of time that satisfies these and all the other corresponding scriptures is exactly 72 hours.
Of course much of the standard thinking on this subject has Jesus dying on Friday evening and being raised on Sunday for approximately 36 hours in the grave – which many do not seem to have a problem with in spite of the pronouncement against a prophet who prophesies and it does not come to pass (Deuteronomy 18:20-22). Try as we may, we cannot come up with three days and three nights much less the 72 hours necessary that Jesus may be proclaimed the Messiah.
The problem lies in the correct determination of which Sabbath immediately followed His crucifixion. We see that it was actually a high Sabbath or a holy day (John 19:31) and not the regular weekly Sabbath. In this case it was the first day of unleavened which follows Passover. Of course this makes perfect sense seeing that Christ was our Passover sacrifice (1 Corinthians 5:7).
In the year of His death this high Sabbath began at sunset on Wednesday evening (when God begins a day). Next we see that the women had to wait until after the end of this Sabbath (Thursday evening at Sunset), to buy spices (Mark 16:1). They prepared them and fragrant oils on Friday and then observed another Sabbath, the weekly one (Friday sunset to Saturday sunset) two days later (Luke 23:56).
Now while it was still dark as the first day of the week (Sunday morning ~6am) began to dawn, the women approached the tomb to find that Jesus had already been resurrected, approximately 12 hours before, (John 20:1; Matthew 28:1-6) proving that He was the Christ.