Just saying those words "a novel in three days" seems like an impossibility to me. I know I could never churn out 60,000+ words in that amount of time. At my current rate of 2,000 words in 90 minutes, that would require 900 minutes (15 hours) at my computer. There's just no way I could hit that. But, for some authors—namely Michael Moorcock—it's a possibility. He could write a 60,000 word sword and sorcery novel (a la Conan) in just three days. Granted, sword and sorcery isn't exactly high literature, but it's still a pretty impressive achievement. Here's the basics of his process (taken from THIS POST, where you can find more details):

1. Have everything prepared.
2. Model the basic plot on the "Quest" theme.
3. The formula depends on the sense of a human being up against superhuman force — politics, Big Business, supernatural evil, etc.
4. Make lists of things you’ll use.
5. Prepare an event for every four pages.
6. Prepare a complete structure. Not a plot, exactly, but a structure where the demands were clear.
7. Prepare a list of images that are purely fantastic, deliberate paradoxes say, that fit within the sort of thing you’re writing. The City of Screaming Statues, things like that.
8. The imagery comes before the action, because the action’s actually unimportant.
9. In your lists, in the imagery and so on, there will be mysteries that you haven’t explained to yourself.
10. Very often a chapter is something like: attack of the bandits —defeat of the bandits.
11. Time is the important element in any action adventure story.
12. Don’t have any encounter without at least information coming out of it.
13. You start off with a mystery. Every time you reveal a bit of it, you have to do something else to increase it.
14. Never have a revelation of something that wasn’t already established.
15. There’s always a sidekick to make the responses the hero isn’t allowed to make: to get frightened; to add a lighter note; to offset the hero’s morbid speeches, and so on.
16. Divide your total 60,000 words into four sections, 15,000 words apiece. Divide each into six chapters.
17. When in doubt, descend into a minor character.
18. Once you’ve started, you keep it rolling.

It's a pretty impressive formula, one that seemed to work wonders for him. After all, EVERYONE who reads fantasy has heard of Elric of Melnibone and his soul-drinking blade Stormbringer (no relation to the Hunter's blade Soulhunger!).