When did the 430 years of Israel's sojourning begin?
That period began when Abram left Haran, while his name was still Abram, after coming up the Euphrates Valley. It ran until the Exodus, divided into 215 years from Abram's entry into Canaan until Jacob entered Egypt, and another 215 years from Jacob's arrival in Goshen until the Exodus.
Les teaches that the 430 years began when Abram, still named Abram, left Haran after traveling up the Euphrates Valley. He divides the period into two 215-year halves: from Abram's entry into Canaan with the promise until Jacob goes from Beersheba to Egypt, and from Jacob's coming into Goshen with Joseph until the Exodus. Les also notes a rabbi's article used the same 215-year figure, and verse 41 says the 430 years ended on the selfsame day.
Now the sojourning of the children of Israel, who dwelt in Egypt, was four hundred and thirty years.
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Were the Israelites in Egypt for the full 430 years?
The 430 years were not all spent in Egypt; the first 215 years were before Jacob entered Egypt, and the second 215 years were from Jacob's entry until the Exodus.
Did Israel leave Egypt on the exact day the 430 years ended?
God's control of time and events is so exact that Israel left Egypt on the very day the 430 years ended, not missing it by 24 hours.