What is the timeline from Adam to Abraham to the giving of the Law?
From Adam to Abraham spans approximately 2,000 years, and from Abraham to the giving of the Law spans about 500 years—more precisely 430 years—making roughly 2,500 years from Adam until Moses received the Law. During that entire period, mankind had no written Law.
Les explains that 2,500 years of human history transpired from Adam until Moses received the Law. Mankind went those 2,500 years without a written Law. He breaks the timeline down as about 2,000 years from Adam to Abraham, then another 500 years from Abraham to the actual giving of the Law. Although the figure is 430 years, Les treats it as round figures—500 years—so the Law was added roughly 2,500 years after Adam.
Wherefore then serveth the law? It was added because of transgressions, till the seed should come to whom the promise was made; and it was ordained by angels in the hand of a mediator.