It took Israel this long to cry out to the Lord. Their response time continues to increase. With Othniel, it was eight years. With Ehud, it was eighteen years. Now it takes them twenty years. This is just one aspect of the downward spiral Israel was on already this early in the book.
3 Then the people of Israel cried out to the LORD for help, for he had 900 chariots of iron and he oppressed the people of Israel cruelly for twenty years.