There are two positions on the time elapsed between Jacob's entry into Egypt and the Exodus:
Short sojourn: 215 years. It implies that the 430-year interval of Ex 12:40 began at Gen ch. 15, as stated by Paul in Gal 3:17.
Long sojourn: 430 years. It implies that the 430-year interval of Ex 12:40 began when Jacob entered Egypt.
Short sojourn position
To note, 215 years is the absolute minimum duration of the Israelites' sojourn in Egypt in the short sojourn position, not the only possible duration. This can be easily seen from Paul's statement in Gal 3:17 - reflecting the view in the proto-rabbinic circle of Gamaliel, under whom Paul had studied the Torah - that the Law had come 430 years after God's promise to Abraham and to his offspring. Now, Abraham's act of faith mentioned in Gal 3:6 and God's promise to Abraham and to his offspring mentioned in Gal 3:16 are in Gen 15:6 and 15:18 respectively, within the event known as "Covenant of the pieces". Therefore we must estimate the time elapsed between Abraham's departure from Haran (Gen 12:4-5) and the promise in Gen 15:18. If, and only if, both events happened within a few months, so that Abraham was still 75 y.o. at the time of the promise, then the time elapsed from Abraham's birth to the Exodus was:
Abraham's birth - Exodus = 75 + 430 = 505 years
Substracting from that the time elapsed from Abraham's birth to Jacob's entry into Egypt:
Abraham's age at Isaac's birth (Gen 21:5)..: 100
Isaac's age at Jacob's birth (Gen 25:26)...: 060
Jacob's age at entering Egypt (Gen 47:9)...: 130
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Abraham's birth to Jacob's entry into Egypt: 290 years
we obtain the absolute minimum short sojourn duration: 505 - 290 = 215 years.
However, the Genesis narrative of ch. 12 to 14 clearly fits better with an elapsed time of several years between Abraham's departure from Haran and the Covenant of the Pieces.
Taking now into account the prophecy in Gen 15:13 that Abraham's offspring ("seed") would serve and be afflicted for 400 years, we can interpret that the servitude and affliction of Abraham's offspring began in any of two moments:
at the feast on the day that Isaac was weaned, when Ishmael mocked Isaac (Gen 21:9), or
at Akedah, when Abraham laid the wood of the burnt offering on Isaac (Gen 22:6) and then bound him and laid him on the altar, on top of the wood, and reached out his hand and took the knife to slay him (Gen 22:9-10). I prefer this interpretation, since this was real servitude and affliction.
Thus, adopting a convention of denoting a specific moment as X.nn, where:
X (or XX) is the initial (or first 2 letters) of the name of a biblical figure or event, and
nn is X's age at that moment if X is a figure, or the number of years that have elapsed from X if X is an event,
we have (with A: Abraham, I: Isaac, J:Jacob, and P:Promise), the following chronology:
A.75. Abraham leaves Haran (Gen 12:4-5)
- a (Time elapsed between Abraham's departure from Haran in Gen 12:4-5 and the promise)
P.0 = A.(75 + a). Covenant of the pieces (Gen ch. 15): Abraham believes the LORD and receives the 400-year prophecy and the promise.
P.(25 - a) = A.100 = I.0. Isaac is born (Gen 21:2-5).
- b (Isaac's age at the event beginning the servitude and affliction of Abraham's offspring prophecied in Gen 15:13)
P.(25 + b - a) = A.(100 + b) = I.b. Either Ishmael mocks Isaac (Gen 21:9) or Abraham offers Isaac in sacrifice (Gen ch. 22).
P.(85 - a) = I.60 = J.0. Jacob is born (Gen 25:26).
P.(215 - a) = J.130. The Sons of Israel enter Egypt (Gen 47:9).
- (215 + a) (Duration of the Israelites' sojourn in Egypt)
P.(430). Exodus
Since the Covenant of the pieces must have been before Sarai gave Hagar to Abram as a wife, which happened "after Abram had lived ten years in the land of Canaan" (Gen 16:3):
0 <= a <= 10
The 400-year interval of servitude and affliction of Abraham's offspring prophecied in Gen 15:13 implies:
400 = 430 - (25 + b - a)
0 = 30 - 25 - b + a
b = 5 + a
Thus we have:
0 <= a <= 10 (Time from Abraham's departure from Haran to the promise)
5 <= b <= 15 (Isaac's age at the event beginning his affliction)
where the values of both variable time intervals move in tandem from left to right within their respective 10-year ranges. Accordingly, the Israelites' soujourn in Egypt may have lasted from 215 to 225 years.
If the event beginning the servitude and affliction of Abraham's offspring prophecied in Gen 15:13 was Akedah, from a practical viewpoint, for Isaac to be able to carry the wood of the burnt offering on top of himself, his realistic minimum age at Akedah is b = 8, so that a = 3, and the Israelites spent 218 years in Egypt. In that case:
Abraham's birth - Exodus = 75 + a + 430 = 508 years
The short sojourn position, both in its usual minimum version or in the adjusted version presented above, fits a literal reading of Moses' genealogy from Levi (Ex 6:16-20), noting that Levi's son Kohath had already been born when Jacob entered Egypt (Gen 46:11). Denoting Kohath's age at the entry into Egypt as KE, Kohath's age at Amram's birth as KBA and Amram's age at Moses' birth as ABM, and knowing that Moses was 80 y.o. at the time of Exodus (Ex 7:7), we have:
Entry into Egypt - Exodus = KBA + ABM - KE + 80
where Kohath's and Amram's begetting ages must be less than their respective lifetimes, and KE must be greater than zero.
KBA + ABM - KE < 133 + 137 = 270
Thus, short sojourn times can be achieved in a number of ways, such as e.g.:
For (KE = 2, KBA = 50, ABM = 90), sojourn time = 218 years
This is fully compatible with Num 3:27-28 stating that the number of male descendants of Kohath was 8600, as e.g. in this way:
Years - Age --- Age ----- Age -- Age -- Kohath's
from -- of ---- of ------ of --- of --- patrilineal
entry - Kohath Jochebed Amram Moses male descendants
0 --- 2 --- .. ---- .. --- .. --- .
30 --- 32 --- 12 ---- .. --- .. --- 3
60 --- 62 --- 42 ---- 12 --- .. --- 3 x 5 + 1 = 16
90 --- 92 --- 72 ---- 42 --- .. --- 16 x 5 = 80
120 --- 122 --- 102 ---- 72 --- .. --- 80 x 5 = 400
150 --- xxx --- 132 ---- 102 --- 12 --- 400 x 3 = 1200
180 --- xxx --- xxx ---- 132 --- 42 --- 1200 x 3 = 3600
210 --- xxx --- xxx ---- xxx --- 72 --- 3600 x 2 = 7200
Long sojourn position
The long sojourn chronology is schematic, intended to assign 1200 years from Abraham's birth to the beginning of the construction of Solomon's temple.
Abraham's birth - entry into Egypt: 290
Jacob's entry into Egypt - Exodus.: 430
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Abraham's birth - Exodus..........: 720 = 60 x 12
Exodus - construction First Temple: 480 = 60 x 8
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Abraham's birth - First Temple...: 1200 = 60 x 20