For how many years did the revelations given to Adam, Eve, Cain, and Abel apply to the whole race?
The revelations given to Adam, Eve, Cain, and Abel applied to the whole race for the first 2000 years, from Adam until Abraham. During that period God dealt with one race, with no organized system of worship, temple, or written law; it was based on conscience and blood sacrifice by faith.
Les explains that from Adam until Abraham, God dealt with one race of people. All the things God had taught Adam and Eve and Cain and Abel were appropriate for that whole race for the first 2000 years. During that time there was no organized system of worship, no temple, and no written law. It was based on man's conscience: if they knew they had sinned, they were to bring a blood sacrifice by faith. If their faith was real, it was their faith that saved them, just as it does today. The human race fell apart until God had no remedy but to destroy them.