I was just reading an article, and now I've lost the link, but it was by Danny Chew, who'd done solo RAAM several times. He said that Enduro required that at certain checkpoints, the riders must stop for at least 5 hrs. He went on to explain that some riders did best when they rested 3 hrs. here and 3 hrs. there, and 5 hrs. at once wouldn't have improved their performance or made things safer. He went into some lengthy discussion about other scenarios and basically challenged the idea that having 5 hr. mandatory rest stops did any good.
Nothing came up on my quick search, but it does seem like Jure Robic had a lot to say about Enduro not being the same race.
I seldom go without 8 hours of sleep each night. I can't imagine at all trying to do 2 or 3 hours here and there. My husband could do it. He's done a lot of shift work over the years and seldom sleeps 8 hours straight through. I'm really impressed by the solo RAAM racers. Don't know how they do it!