I saw your ride report on it; it was actually how I learned about the ride in the first place. You peaked my interest in it.
30 hours just seemed like a strange time figure, seeing as how a BB1500 is either 36 or 24 hours. The I-20 E2E seems to split the difference. I was curious about the official rationale.
Perhaps because over a third of it, approximately, is 80 mph speed limit? The rules for a BB1500 or BBG are designed to work with any part of the country, not a dedicated route, (imho), whereas the E2E routes are dedicated routes with known issues and lack there of.
636 miles of the route is in Texas (the only state in the route with a speed limit over 70). Assuming zero delays and gas stops, it'd take 7.95 hours at 80 mph or 9.1 hours at 70 mph, so only a little over an hour difference.
I suppose that ultimately it doesn't matter, since I'll do it in the prescribed time frame anyway. I was just curious about the reasoning behind the time difference.