Just wondering how long before it changes?

It changes instantly -- but I see the username I'm pinging isn't the one I'm reading on the OP, haha. It must be the cache, it could take a couple hours but a few minutes should hopefully be enough for it to update (:

[edit] There you go, changed for me. xD

In the time it took me to ask the question then go get a drink it changed now I just feel silly. Thank you for your help I'm really sorry to waste your time.

No worries, it's no problem at all! There's still a lot of cache delay all around the site, sadly, but normally it sorts itself out fairly quickly. Enjoy your new username! ^_^