215 Years or 430 Years?
"The statement in Exod 12:40 that the people of Israel dwelt in Egypt for 430 years is also not without question. [footnote: The figure of 400 years for the same period found in Gen 15:13 (MT and LXX), in Acts 7:6 and in Josephus (Ant. 2,204; War 5.382), is most simply explained as a round number for the 430 figure. For a more complex assessment see Harold Hoehmer, "The Duration of the Egyptian Bondage", BSac 126 (1969): 308-316.)"
"If, however, a shorter and presumably more realistic estimate is made of the probable length of these generations [Bezalel; Elishama; and Joshua] a shorter sojourn can be supposed. A shorter genealogical sequence which also can point to a shorter sojourn is found in Exod 6:16-20 ... we are not told the age of Kohath when he went down into Egypt, if we suppose that his grandson, Moses, was born 80 years later, and if Moses was 80 years old al the exodus (Exod 7:7), we have a total of only 160 years for the sojourn in Egypt."
"In Exod 12:40 an actual textual variant in the Septuagint adds several words, so that the statement reads 'The time that the people of Israel dwelt in Egypt and the land of Canaan was four hundred and thirty years.' ... the Alexandrian-Jewish chronographer Demetrius (before 200 B.C.) ... understood that there was an exact division of the 430 years into 215 years in Canaan and 215 years in Egypt. The LXX text is apparently reflected also in Gal 3:17 which makes the 430 years cover the time from the promises from Abraham to the exodus and the giving of the law. Similarly, and perhaps in dependence upon Demetrius, Josephus states in one passage (Ant. 2:318) that the Israelites left Egypt '430 years after the coming of our forefather Abraham to Canaan, Jacob's migration to Egypt having taken place 215 years later.'"
"Gerhard Larsson (whose comparison of chronology in the MT and LXX indicates that alterations in the LXX are at points where the MT is difficult to understand or self-contradictory) finds a 430-year sojourn-period 'impossible', in the light of the Kohath/Amram/Moses sequence, and concludes that 'at most the period [of the sojourn] could be little more than 300 years' (footnote: Larsson, JBL 102 (1983) : 406). ... for the sake of an interesting possibility in connection with Joseph in Egypt we will add 14 years ... and set down the figure of 314 years."
The "connection with Joseph" mentioned above lines the biblical chronology up with an Egyptian manuscript, the Book of Sothis.
The above is taken from paragraphs 358-363 in Handbook of Biblical Chronology, by Jack Finegan (revised edition, 1999.
