Genesis 1 describes the completion of each day's creative acts by God with the words: there was evening and there was morning, the nth day. Some commentators have argued that the day began at evening and Genesis is saying that the beginning of the day is at evening, then morning occurred, and the day therefore ended at the next evening. This sounds strained. Evening and morning occur after the creative act. It seems more logical to read the verses as saying that the creative acts occurred during the daylight followed by evening after the creative acts have finished* followed by night followed by the next morning which is the terminus of the day.
And God said, “Let the waters swarm with swarms of living creatures, and let birds fly above the earth across the expanse of the heavens.” So God created the great sea creatures and every living creature that moves, with which the waters swarm, according to their kinds, and every winged bird according to its kind. And God saw that it was good. And God blessed them, saying, “Be fruitful and multiply and fill the waters in the seas, and let birds multiply on the earth.” And there was evening and there was morning, the fifth day. (Gen 1:20-23)The day begins at dawn, then God creates the fish and birds, then the evening comes, and then the day completes with a new morning.
I suspect that this was the case at creation and was still in place at the time of the Exodus. That is, the Hebrew day started at dawn and finished the following dawn. A transition to a calendar where the day commences at dusk occurred sometime later: prior to the current era, possibly before the time of Jesus; perhaps around the time of the Exile to Babylon. There is evidence of a different possible calendar change at the time of the Exile: the year start switched from the first month (Nisan) to the seventh month (Tishri).
If the day started at dawn, at least from the time of creation to the exodus, there could be evidence of this in Scripture.
I would argue that the instructions concerning Passover and Unleavened Bread make the most sense if the day commenced at dawn. I will call a day commencing at dawn a dawn-day. That is, at dawn when the sun comes up a new day begins. Likewise dusk-days commence in the evening.
English Bibles often use the term "twilight" whereas the literal text uses the phrase "between the evenings". There is considerable debate about what this phrase means. It may be that the first evening occurs when the sun goes down and the second evening when it gets dark. Or from sundown to midnight. Or from noon until sundown. Perhaps even between noon and midnight. For the passages we will discuss the interpretation does not significantly affect our calculations.
There are three instructions concerning the Passover and the Feast of Unleavened Bread. These occur in Exodus, Leviticus and Numbers. These instructions were all given during the same epoch which means that the time the day began was almost certainly the same for all three episodes. This is unless Exodus uses an Egyptian calendar which changed after the Hebrews left Egypt.
God gave Moses instructions for the Passover,
Yahweh said to Moses and to Aaron in the land of Egypt, saying, “This month [Abib, Nisan] will be the beginning of months; it will be for you the first of the months of the year. Speak to all the community of Israel, saying, ‘On the tenth of this month, they will each take for themselves a lamb for the family,...Passover was on the fourteenth day of Nisan. The Feast of Unleavened Bread was for seven days. They were to start eating the unleavened bread on the evening of Nisan 14 and continue until the evening of Nisan 21.
“You will keep it until the fourteenth day of this month, and all the assembly of the community of Israel will slaughter it between the evenings... And they will eat the meat on this night;...
“And I will go through the land of Egypt during this night, and I will strike all of the firstborn in the land of Egypt,...
“And this day will become a memorial for you, and you will celebrate it as a religious feast for Yahweh throughout your generations; you will celebrate it as a lasting statute. You will eat unleavened bread for seven days. Surely on the first day you shall remove yeast from your houses, because anyone who eats food with yeast from the first day until the seventh day—that person will be cut off from Israel. It will be for you on the first day a holy assembly and on the seventh day a holy assembly; no work will be done on them; only what is eaten by every person, it alone will be prepared for you.
“And you will keep the Feast of Unleavened Bread, because on this very day I brought out your divisions from the land of Egypt, and you will keep this day for your generations as a lasting statute. On the first day, on the fourteenth day of the month, in the evening, you will eat unleavened bread until the evening of the twenty-first day of the month. For seven days yeast must not be found in your houses, because anyone eating food with yeast will be cut off from the community of Israel—whether an alien or a native of the land. You will eat no food with yeast; in all of your dwellings you will eat unleavened bread.” (Exo 12)
In Leviticus God gives further instructions,
These are Yahweh’s appointed times, holy assemblies, which you shall proclaim at their appointed time. In the first month, on the fourteenth of the month at the evening is Yahweh’s Passover. And on the fifteenth day of this month is Yahweh’s Feast of Unleavened Bread; for seven days you shall eat unleavened bread. On the first day there shall be a holy assembly for you; you shall not do any regular work. And you shall present an offering for Yahweh made by fire for seven days; on the seventh day there shall be a holy assembly; you shall not do any regular work. (Lev 23:4-8)This reiterates the command in Exodus but clarifies that Passover is on Nisan 14 and the Feast of Unleavened Bread begins on Nisan 15. Exodus states that unleavened bread is to be eaten from Nisan 14, that is from Passover proper; yet they are to eat it for 7 days. Leviticus states that the Feast of Unleavened Bread proper starts on Nisan 15.
Again, in Numbers, at the end of 40 years of wandering, God commands,
On the fourteenth day of the first month is the Passover for Yahweh. On the fifteenth day of this month is a religious feast, unleavened bread must be eaten for seven days. On the first day there will be a holy assembly you will not do any regular work.... On the seventh day you will have a holy assembly you will not do any regular work. (Num 28:16-18,25)These passages give similar commands. What is notable is that while all three give 7 days as the duration of the Feast of Unleavened Bread, Exodus specifies that this is to be from the evening of Nisan 14 to the evening of Nisan 21. There is also to be a holy assembly on the first and seventh days of Unleavened Bread.
Using dawn-days we have Nisan 14 starting in the morning and the passover lamb being killed between the evenings (ʿereb) and eaten that night (layil). Unleavened bread would be eaten that evening with the Passover meal (Exo 12:8,18). The following morning starts the next day: Nisan 15. Nisan 15 is the first day of the Feast of Unleavened Bread when they have a holy assembly with the attendant sacrifices. Nisan 16 is day 2 of the feast, Nisan 21 is day 7. There is a holy assembly that day also. In the evening the feast ends and unleavened bread only needs to be eaten until that evening (Exo 12:18).
|evening||Passover sacrifice||unleavened bread begins|
|Nisan 15||morning||Feast Day 1||holy assembly|
|Nisan 16||morning||Feast Day 2|
|Nisan 17||morning||Feast Day 3|
|Nisan 18||morning||Feast Day 4|
|Nisan 19||morning||Feast Day 5|
|Nisan 20||morning||Feast Day 6|
|Nisan 21||morning||Feast Day 7||holy assembly|
|evening||unleavened bread ends|
Using dusk-days the entire feast of Passover and Unleavened Bread must last 8 days. Nisan 13 changes to Nisan 14 at dusk. The lamb is slaughtered and eaten that night along with unleavened bread. In the morning it is still Nisan 14 which is still Passover day. The Feast of Unleavened Bread does not start until that evening Nisan 15 (Lev 23:6). The holy assembly occurs that day but not until the following morning because they were not to work and the sacrifice of the first day of Unleavened Bread occurs at the same time as the morning sacrifice (Num 28:23).
Nisan 15 is the first day of the feast and Nisan 21 the seventh day. Nisan 21 starts in the evening but the evening of Nisan 21 is also when the the consumption of unleavened bread ceased. From the evening of Nisan 21 the Israelites were no longer required to eat unleavened bread even though the Feast of Unleavened Bread still had one day to go. The following morning they had the holy assembly on the final day of the feast. If unleavened bread was to be continued to be eaten until the end of Nisan 21, just before Nisan 22 started, then the command to eat for seven full days (Exo 12:19) is actually eight full days.
|Nisan 14||evening||Passover sacrifice||unleavened bread begins|
|Nisan 15||evening||Feast Day 1|
|Nisan 16||evening||Feast Day 2|
|Nisan 17||evening||Feast Day 3|
|Nisan 18||evening||Feast Day 4|
|Nisan 19||evening||Feast Day 5|
|Nisan 20||evening||Feast Day 6|
|Nisan 21||evening||Feast Day 7||unleavened bread ends|
All three passages concerning Passover and the Feast of Unleavened Bread make sense if the Israelites were using dawn-days. Dusk-days imply that there is a morning after Passover begins prior to the holy assembly, and that the second holy assembly occurs after the time of unleavened bread ceases.
*This may not be the case on day 2.