What is the whole point of all this? Why does it change anything? What are you trying to prove here? Forget about Matt 12:40; if it bothers you.
At least 8 other verses say it was the third day. A day can be 12 hours, a night can be 12 hours. Together they can be 24 hours.
Matt 12:40; for just as JONAH WAS THREE DAYS AND THREE NIGHTS IN THE BELLY OF THE SEA MONSTER, so will the Son of Man be three days and three nights in the heart of the earth.
Jonah 1:17; And the LORD appointed a great fish to swallow Jonah, and Jonah was in the stomach of the fish three days and three nights.
Mark 8:31; And He began to teach them that the Son of Man must suffer many things and be rejected by the elders and the chief priests and the scribes, and be killed, and after three days rise again.
John 2:19; Jesus answered them, "Destroy this temple, and in three days I will raise it up."
Matt 16:21; From that time Jesus began to show His disciples that He must go to Jerusalem, and suffer many things from the elders and chief priests and scribes, and be killed, and be raised up on the third day.
Matt 17:22; And while they were gathering together in Galilee, Jesus said to them, "The Son of Man is going to be delivered into the hands of men;
Matt 17:23 and they will kill Him, and He will be raised on the third day." And they were deeply grieved.
Luke 18:32; "For He will be handed over to the Gentiles, and will be mocked and mistreated and spit upon,
Luke 18:33; and after they have scourged Him, they will kill Him; and the third day He will rise again."
Luke 24:6; "He is not here, but He has risen. Remember how He spoke to you while He was still in Galilee,
Luke 24:7; saying that the Son of Man must be delivered into the hands of sinful men, and be crucified, and the third day rise again."
Acts 10:39; "We are witnesses of all the things He did both in the land of the Jews and in Jerusalem. They also put Him to death by hanging Him on a cross.
Acts 10:40; "God raised Him up on the third day and granted that He become visible,
It doesn't look like anyone here on TalkJesus other than yourself thinks it was anything besides 3 days.
Even "IF" Jesus was dead 6 days (I don't believe he was but..) it wouldn't be the crucifixion that happened 6 days later. It would be the resurrection.