We closed on a resale purchase August 21st and just got our membership cards this week. Yesterday we received the postcards with the online registration code. Don't wait for these to come, it takes forever. Just call and they'll be happy to give you the code over the phone so that you can log on.
And if the person you speak to at Member Services says that he can't give you the Club ID and the one-time password (or whatever they call it) to get on the website, hang up and call again. That happened to me. First person said he couldn't give it to me; second person did.