Is it duplicate content if you take a site down before republishing elsewhere?

[Jake]

There is probably some overlap time while the cashed copy of the old site is still around. The most common strategy involves using a 301 permanent redirect to signal the search engine that the site has been relocated, re-rout traffic as well as link juice to the new site.

I have to guess that even if you remove the original site after the new one is up that the new one will still get top priority after the old one is removed (Have you checked if anyone else has already duplicated your stuff?)