Okay, so the world record pace is something like 4:42 per mile. How long would it take you to run that pace for full 26.2 miles not counting rest breaks.
You can break it up any way you want to.
I'll admit that I can't currenly run 4:42 for even one mile. 2:21 for a half mile would be doable but it would likely take me several days total to get in 52+ reps of half mile repeats in that pace.
I think the best bet for me would be to break it into 400 meter repeates. Maybe occasionally change up the distance between 200 and 600 just to get something a little different.
By structuring it that way, I'm pretty sure I could finish 26.2 total miles at World Record pace in less than 24 hours.