Yes, I think importance outweighs chronology here in terms of traditional resume writing.
Nano is an important exercise but in the end that's what it is. It shows a skill that you have, but it's a personal win and not a traditional type contest where you've won out over others. Doesn't hurt to put it on your resume but an actual publication credit definitely is more impressive and you don't want to give the impression that you're making Nano into something that it's not.
Edit: Just saw Veinglory's post and I would say that it depends on the job you're applying for. In a sense, yes, this category that you're adding into your resume IS similar to a hobbies and interests section because you really don't have a lot of "professional" writing experience, so anything goes as far as I'm concerned. If you had several publications in good literary journals, I'd say don't mention Nano at all, but in this case I don't think it would hurt. Just my opinion, of course.