Personally, I've found that there is a brief window available right after maintenance or patch day. But, be careful. Since the site is only updated every so many hours, it's not always up-to-date with the actual game. The page might say that a wold server is accepting new characters, but when you go to start a new game with said character, you learn that the server isn't accepting new characters.

Quote Originally Posted by Vespar View Post
Wow, Japan's data centers seem maxed and as of my post its 4:15AM over there. Wonder why they haven't created new servers there...
It happens every once in a while, but it's often NA/EU world servers that are not accepting new characters.