How many years were there between God's promise to Abraham and the giving of the Law at Sinai?
The interval was 430 years. Paul states that the covenant confirmed beforehand by God in Christ could not be annulled by the Law, which came 430 years later. Israel came out of Egypt and received the Law at Sinai four hundred thirty years after the promise to Abraham.
Les explains that the Law was itself a covenant, just as the Abrahamic and Davidic covenants were covenants—agreements God made that He could never change or withdraw. He notes that this covenant, the Law, came 430 years after God's promise to Abraham that the seed would come through him. At that 430-year mark, Israel came out of Egypt and received the Law at Sinai. Les also addresses the scoffer's claim of contradiction because other passages mention 400 years and 490 years, but he insists there is no contradiction and points back to Genesis.
And this I say, that the covenant, that was confirmed before of God in Christ, the law, which was four hundred and thirty years after, cannot disannul, that it should make the promise of none effect.
And he said unto Abram, Know of a surety that thy seed shall be a stranger in a land that is not theirs, and shall serve them; and they shall afflict them four hundred years;