The answer is never. Deleting a WordPress.com blog is not easily done. To prevent accidental or inadvertent deletion of blogs, there are multiple warnings given that blog deletion is permanent. Deleting a site permanently removes it and you’ll never be able to reuse its WordPress.com address. If you delete a blog you will not be able to get it back and no one else will be able to use that blog address. You must be sure you never want to use the blog again if you delete it. Lastly, a verification link is sent in an email and must be clicked to delete a blog. http://en.support.wordpress.com/delete-site/
You ignored the warnings and clicked the verification link so the URL is gone. Deleted blog URLs are not recycled, regardless of who registered and deleted them and no exceptions are made.
You can register another blog with a similar name. http://en.support.wordpress.com/register-a-blog/
Or you can register a domain via a domain mapping upgrade and it will not matter what the underlying .wordpress.com address is.