There are many debates regarding what God means by “three days” in the bible, in reference to the death and resurrection of Jesus Christ.
It's always the easy route to think that the way we do things is the way everyone else does it; but that isn't necessarily so!
So let's look at two or three places in the bible where the third day from 'today' is counted off so that we can see what was in God's and the Israelite's minds!
Take Exodus 19 verses 10-11. This is the point in time where Jehovah is going to give Israel the ten commandments. He personally gives them this instruction through Moses...
Exo 19:10-11 And Jehovah said to Moses, 'Go to the people and sanctify them today and tomorrow, and let them wash their clothes. And be ready for the third day. For the third day Jehovah will come down in the sight of all the people upon Mount Sinai.
So according to God himself, starting from 'today', Jehovah thinks the third day is the day after tomorrow! Check it out above again! Sanctify them today, and tomorrow and be ready for the third day! When counting from 'today' God in effect calls 'today' – Day 1!
That's one example and one might wonder if it's an isolated one but looking around in the bible I found this in Luke 13, 31-32.
At that very hour some Pharisees came and said to him, “Get
away from here, for Herod wants to kill you.
So in this direct quote from Jesus where he counts off what he means by the third day, Christ also thinks that starting from today the third day is once again the day after tomorrow! So that's one example from the mouth of Jehovah and the other from the mouth of Jesus.
Interestingly while I was looking into these two examples I also found another one that was said out of the mouth of an ordinary human being in the time of Jesus. This I noted in the book of Luke, Chapter 24, verses 20-21. And this one I could use to work backwards to the day of Jesus' death using Jehovah and Jesus' timing system!
Luk 24:20-21 …and how the chief priests and our rulers delivered Him to the judgement of death, and have crucified Him. But we had trusted that He was the One who was about to redeem Israel. And besides all this, today is the third day since these things were done.
And the last thing mentioned is Jesus being crucified.
Now there can be many new human reasons based on how we count time today which we can use to come up with other end days for the time from 'crucifiction to resurrection' but it does seem that according to God and Jesus' manner of counting, Friday to Sunday is the one that fits!