How are the 430 years from Abraham divided between the time before Egypt and Israel's slavery in Egypt?
The 430 years are divided into two equal 215-year periods: the first 215 years run from Abram until Jacob goes down into Egypt with his offspring, and the second 215 years cover Israel’s time in Egypt under slavery. Together these two periods fill the full 430 years.
Les explains that God’s timetable is exact: when He told Abram it would be 430 years, that is exactly what it was. From the time Abram had Isaac until the tabernacle was raised up at Mount Sinai, and they were ready to go up into the promised land, was exactly 430 years. Within that time period, 215 years go from Abram until Jacob goes down into Egypt with all his offspring, and another 215 years are spent in Egypt under slavery. Those two 215-year spans fill the 430 years.