Let me illustrate this another way.
Mat 12:38 Then some of the scribes and Pharisees said to Him, "Teacher, we want to see a sign from You."
Mat 12:39 But He answered and said to them, "An evil and adulterous generation craves for a sign; and yet no sign will be given to it but the sign of Jonah the prophet;
Mat 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.
You're saying that Jesus Christ was basing his messiahship on an idiom who's exact time length was unknown AT THE TIME. Or, you're saying that the Pharisee's understood that Jonah was NOT in the fish three days and three nights, but instead was only in there 2 nights and 1 day. How they knew this without Christ being dead in the grave is a mystery indeed.
"Teacher, we want to see a sign from You."
Yeah....that's always been an amazement to me also...his one and only sign proving his Messiah ship.....and some folks think he meant only a day and a half. Three days and three nights does not line up with their tradition. But....most other scripture does not line up with their tradition either. Why should I express surprise?
Blessed Sabbath to you Douglas.