I believe what Kart Racer is trying to say is:
There would be an Eastern Division that would be able to race a little earlier, and a Western Division that would be able to race later. When you would want to race (time-wise) would be up to you. You don't necessarily have to enter the Eastern Division if you want to race later in the evening. You could live on the East Coast and race with the Western Division racers.
That would allow for an option of selecting an earlier start time for the Eastern Division, and would separate the Time constraint issues. You would, however need to declare the division in which you would want to race.
This is merely a method to allow the western Side of the countries the ability to start a little later, which would allow for the time necessary to tune a car and test run it after the dinner hour, rather than before.
Please correct me if I am wrong on this, Kart.