Your objection is a fair one, but having come into the company through the process I describe I am fond of how it let me (a) show that I could actually do the stuff I claimed to be able to (b) show my thought processes and how I would deal with having received a box in this condition. So I was quite pleased to do it as a candidate. Certainly less of a waste of time than a clashing interview.
The way I do this is the real coding test is only administered to final candidates. That's a bit kinder since only a few people with a serious shot at the position end up having to commit the extra time and since we observe the whole process (and discuss) it doesn't waste tons of our time either. Whiteboard and discussion can reveal a lot but IMO there's nothing so revealing as actually watching someone work.
As an aside I would much rather be interviewed this way than at a whiteboard. At least for me there's a certain amount of my programming skill that's nonverbal and flows easier for me at a keyboard.
A cook is someone who can be hired with very little experience. A chef is someone who is trained professionally. And plenty of chefs are hired without a "taste test" based on their academic and employment history.
They're hired on a provisional basis, true, but they are paid while they prove themselves.
So in the end you're only hurting yourself because you'll mostly get naive and easily manipulated people who are fine for the lower ranks but absolute poison once they move up. That's if they don't wise up and leave first, costing you time and effort to find and train replacements and scramble to rediscover and distribute the lost knowledge they left with.
But then again, such a long duration challenge is already very telling of the company culture. If you can't respect other peoples' time, then your company is already on shaky footing.
These things shouldn't be designed to take 14 hours. They should be designed to take one, maybe two or three . . . if you know what you're doing.
One of the other posters took so long because he didn't know what he was doing. Well, perhaps that is an uncharitable way to say it, but you know what I mean. :)
Yeah but how many questions must you ask before you are certain? Otherwise you're rolling the dice that the candidate has simply seen that problem before but has terrible habits otherwise.
Reduce the time required and you risk more false positives. Increase the time required, and you risk the skilled ignoring you.
And if your "technical grilling" fails to identify strong candidates, you're obviously asking the wrong questions or, at the very least, not asking the right ones.