The Iniquity of the Amorites Is Not Yet Complete

The Lord is speaking to Abram and he says, they shall come back here in the fourth generation for the iniquity of the Amorites is not yet complete. It seems to me that the Lord has an appointed amount of sin that he is going to allow the Canaanites to commit. And then once they have filled up the measure of their sins just that moment, the Lord will have brought Israel out of Egypt with God's wrath on them.