Soon as I get it setup on this end, you can transition the nameservers. Those changes supposedly take 24-48 hours, but in reality I usually see them hit within the hour. Assuming you have the same site mirrored at both locations, the actual transition would be seamless to users. A user would be sent to the old site, then whenever the change makes it to their server, the next page they view would be sent here. They wouldn't notice a thing.
On that note, I've set up things at this end, so go ahead and set the nameservers to ns1.xepher.net and ns2.xepher.net whenever you're ready.