1) As long as there hasn't been any public notice of your funding (from your VC's blog, an errant mention in a a round-up article, or even a tweet), you can make the announcement when it's most advantageous. Journalists don't care about when the actual round was closed as much as that it hasn't been covered yet.
That being said, if it did happen a while ago and a journalist happens to connect the dots and ask why you waited so long to announce, you should have a good reason prepared. We've never seen it be an issue.
2) You definitely should try! It just means there's less of a guarantee the news will be covered. We've seen funding announcements of as little as $500k get covered. In these cases though, it helps to have another piece of news to include: a substantial product release, a notable new advisor, a major partnership, etc.