It's always come off instantly for me. But only if you provide the exact correct URL. So if you have a dev version in:
http://mydomain.com/dev
Then you need to use that entire URL for the license location, then hit register and it comes off immediately. Now, if you decide to move it out of "dev" and into the root to go live, you can just change the URL in X-Cart Support Desk after you go live.