7:15 This text shows additional evidence that for the purposes of these sacrificial offerings, the day was reckoned from daybreak to daybreak. The commandment is that it shall be eaten on the day of his offering; he shall not leave any of it until morning. The parallel commandment he shall not leave any of it until morning (עַד־בּוֹקֶר) marks the end of the day at daybreak. If the day had ended at sunset, then the commandment would say, "he shall not leave any of it until sunset". Daybreak to daybreak is the default method of counting a day in the Scripture (except for Sabbaths). See Genesis 1:5 note. Any other explanation requires further ad hoc (unparsimonious) assumptions.
Since the text says in the day, בְיוֹם, it is clear that the limit up to morning is reckoned as the same day, and not two days broken by sunset. The breaking point between day's is daybreak. Even the Rabbis are compelled to recognize that the calendar day is reckoned to end at morning here because in the Talmud they legislate that the "peace offering" cannot be eaten after midnight. They put this fence up before the morning limit so as to prevent Israel from tempting the morning limit of the calendar day by coming too close to it.
Rashi's commentary says, "וּבְשַׂר זֶבַח תּוֹדַה שְׁלָמָיו — And the flesh of the sacrifice of His thanksgiving peace-offering. יֵשׁ כַּאן רִבּוּיִין הַרְבֵּה — There are many inclusions here, ... to include the sin-offering, ... and the guilt offering, ...and the ram of the nazir, ... and the festival-offering of the fourteenth of Nisan, ... that they should be eaten לְיוֹם וָלָיְלָה — for a day and a night, the day of the sacrifice and the night which follows" (pg. 76-77, The Sapirstein Edition, Rashi, Vayikra/Leviticus). And all of this is reckoned as in the day of his offering.
We can apply this Messiah's offering, and the chronology of his death and resurrection. The day for a sacrifice is reckoned from daybreak to daybreak, (a day and then a night), for the passover offering, for the sin offering, for the peace offering, for the festival offering, etc. (cf. Rashi above). Yeshua fulfilled all these types. The day of His offering is counted from daybreak Wednesday to daybreak Thursday. The second day is daybreak Thursday to daybreak Friday, and "the third day" is daybreak on the sixth day to daybreak on the Sabbath. Yeshua was raised from the dead at "deep dawn" on the first Sabbath after the Passover (see John 20:1), "in the third day" (Hosea 6:2), which day is the calendar day from daybreak to daybreak for the first fruits offering.
"According to y.Berachot 9b [cf. m.Berachot 1.1], which is discussing the sacrifices which must be eaten on a single day, the day consists of the daylight in which the offering is made and the night which follows. Thus, one may eat the meat of such a sacrifice throughout the night until the dawn appears. But the Sages, in order to make a safe-guard, ruled that such meat should not be eaten after midnight. Still, if one did eat past midnight, he did not violate a biblical commandment but only a rabbinical one:" (Tim Hegg, "The Chronology of the Crucifixion: A Comparison of the Gospel Accounts", 2009).
Jacob Neusner translates for us:
"1:1 A. From what time may they recite the Shema in the evening?
B. From the hour that the priests enter [their homes] to eat their heave offering,
C. "until the end of the first watch"—
D. But sages say, "Until midnight."
F. Rabban Gamaliel says, "Until the rise of dawn."
G. M‘SH Š: His [Gamaliel's] sons returned from a banquet hall [after midnight].
H. They said to him, "We did not [yet] recite the Shema."
I. He said to them, "If the dawn has not yet risen, you are obligated to recite [the Shema].
J. "And [this applies] not only [in] this [case]. Rather, [as regards] all [commandments] which sages said [may be performed] 'Until midnight," the obligation [to perform them persists] until the rise of dawn."
K. [For example,] the offering of the fats and entrails—their obligation [persists] until the rise of dawn [see Lev. 1:9, 3:3-5].
L. And all [sacrifices] which must be eaten within one day, the obligation [to eat them persists] until the rise of dawn.
M. If so why did sages say [that these actions may be performed only] until midnight?
N. In order to protect man from sin." (The Mishnah: A New Translation, by Jacob Neusner, page 3).
23:5a בין הערבים = between the settings. The first setting of the sun begins at noon when it begins to decline, and the second setting is at sunset. The time defined is the period between these two critical points of setting. The whole period of time that the sun goes down is also called ערב, which is the time from noon to sunset.
23:6a The 15th day here is defined as from sunset at the end of the 14th day till sunset at the end of the 15th day.