1. The Messiah said that three nights would be involved with His time in the "heart of the earth".
Having been raised for a few years by my aunt as a JW, but being born a Jew and today back to being a practicing Jew, I can assure you that as many times that I've heard that "heart of the earth" is supposed to be some Jewish idiom, it is not.
There is no such saying or expression in any Jewish language like that which is an idiom of any sort, not in Hebrew, not in Ladino, Yiddish, Aramaic or Arabic. We don't have such a common expression in any of our modern languages or in modern Hebrew either. I am a Sephardic Jew, and I speak Ladino and Hebrew throughout my day (and some Yiddish). I have verified this with many a rabbi and scholar, and there is no such idiomatic expression as many a Fundamentalist Evangelistic Christian claims.
It should be noted, however, that the contrast is with Jonah not being in the belly of the fish, but Jonah recognizing that the fish was swimming deep into the depths of the waters, which Jews viewed as the Netherworld of the Dead or Sheol. Jonah thus refers not to the belly of fish as Sheol but to traveling down into Sheol by means of the fish's belly.--Jonah 2:2.
Jesus is saying he, like Jonah, would spend three days and nights (according to Jewish reckoning) in the Netherworld.
4. However, those two beliefs allow for only 2 nights to be involved.
While I am not a Christian, and I definitely do not believe that Jesus of Nazareth was the Messiah, and on top of that reject the idea of the Resurrection of Jesus, Jews can say "three days have passed" but only two nights have occurred. This has been common speech for Jews for thousands of years and still is to this day.
For instance, tonight is the start of Chanukah. Jews, like me, are celebrating by lighting their first candles in their windows all around the world. But your calendar may say different if you're a Gentile. It may say Chanukah starts tomorrow.
Well, that is true too. You see the first day of Chanukah is tomorrow because our days start at sundown and end at sundown. If you use a Gentile calendar, the first day of Chanukah is December 13. If you use a Jewish calendar it begins on December 12.
If you use the Gentile day of reckoning and count three days of Chanukah, let's say December 13-15 you get three days but only two nights of candle lighting. Why?
Because the Jewish candle lighting for the 13th was on the 12th and the candle lighting for the 15th counts as the Erev or eve of the 16th of December. According to Jewish counting there were three days but only two nights. Get it?
So if Jesus was the Messiah, and if he did rise from the dead, he could have died on a Friday and risen Sunday. The colloquial speech works with Semitic dialogue about counting days. All the other stuff you wrote is just Gentile/Christian/Gregorian calendar fluff.
People always want to make Jesus of Nazareth fit into a Christian mold. If he was the Messiah, remember, "messiah" is a Jewish concept. To understand it fully you have to let go your Gentile self.