This might help explain how this works. Clearly whatever day Yeshua died (and I believe it was a Friday), the exact 72 hours calculation will never work. He died in the afternoon, and rose before morning.
During an online debate with Christians about the above Scripture verse, an unlikely contributor to the debate showed us something that I'd heard before, but had never seen proven. Joe Zias, ex-curator of the Israel Museum in Jerusalem, an archaeologist with the Israel Antiquities Authority, and a Jewish man who does NOT believe that Jesus rose from the dead or is the Messiah, nevertheless weighed in with a post about the idiomatic use in Jewish circles of the phrase "three days and three nights." In brief, Zias said that the phrase is found elsewhere in the Bible and in Rabbinic literature, and that it did not usually refer to a literal 72 hour period of time. He said, "It's one example of many Hebrew idioms used for inclusive time reckoning."
A literal interpretation by some well-meaning Christians, of the phrase "three days and three nights" as representing an exact period of 72 hours, displays ignorance of the biblical and rabbinic evidence about the idiomatic use of the phrase "a day and a night," of which "three days and three nights" is merely an expansion. In truth, the idiom refers not to an exact number of hours or of minutes, but simply to a calendrical day, whether complete or incomplete.
In the Bible, a fraction of a day or of a night was reckoned inclusively as representing the whole day or night. This method of reckoning is known as "inclusive reckoning."
[See: this link Ortho ].
A few examples from the Bible and from rabbinic literature will suffice to demonstrate its usage (I am indebted to Samuele Bacchiocchi, Ph. D., Andrews University from his book The Time of the Crucifixion and the Resurrection for the following examples and most of the commentary):
1Samuel 30:12 speaks of an abandoned Egyptian servant who "had not eaten bread or drunk water for three days and three nights." The idiomatic usage of this expression is shown by the following verse, where the servant states that his master had left him behind "three days ago" (v. 13). If the "three days and three nights" were meant to be taken literally, then the servant should have said that he had been left behind four days before.
Esther 4:16 mentions that when Queen Esther was informed by Mordecai about the plan to exterminate the Jews, she sent this message to him: "Go, gather all the Jews to be found in Susa, and hold a fast on my behalf, and neither eat nor drink for three days, night or day. I and my maids will also fast as you do. Then I will go to the king." However, we read in 5:1 that Esther went before the king "on the third day." If Esther intended the three days and three nights to be taken literally as a 72-hour period of fasting, then she should have presented herself before the king on the fourth day. These two biblical examples clearly show that the expression "three days and three nights" is sometimes used in the Scriptures idiomatically to indicate not three complete 24-hour days, but three calendric days of which the first and the third could have consisted of only a fraction of a day.
But we also have examples from ancient rabbinic literature. For instance, Rabbi Eleazar ben Azariah, who lived about 100 CE, said, "A day and a night are an Onah [‘a portion of time’] and the portion of an Onah is as the whole of it." (As quoted from the Jerusalem Talmud, Shabbat 9,3; see also Babylonian Talmud, Pesakhim 4a; and the Midrash Rabbah on Genesis 56.1 (commenting on Gen 22:4); Genesis 91.7 (commenting on Gen 42:17-18); Esther 9.2 (commenting on Esther 5:1). Etc. In fact, according to The Jewish Encyclopedia, a standard Jewish reference work [available for perusal online here: ], the practice of inclusive day reckoning is still in vogue among the Jews today.
"In Jewish communal life part of a day is at times reckoned as one day; e.g., the day of the funeral, even when the latter takes place late in the afternoon, is counted as the first of the seven days of mourning; a short time in the morning of the seventh day is counted as the seventh day; circumcision takes place on the eighth day, even though on the first day only a few minutes remained after the birth of the child, these being counted as one day." ("Day," vol. 6, p. 475). In fact, Joe Zias used the example of “the eighth day” regarding circumcision not necessarily being eight full days. He, being an Israeli Jew, drew it from his own personal experience with inclusive day reckoning.
The examples cited above give sufficient evidence that in biblical times (and until now) the expression "a day and a night" could mean idiomatically "a day," whether complete or incomplete. Thus, in the light of the prevailing Jewish usage, Jesus employment of the expression "three days and three nights" in Mat 12:40 does not necessarily require that Yeshua would have been entombed for 72 hours. Rather, a full day and two partial days fit the time-frame best, as ancient Christian tradition has historically understood it.