Gilgamesh tends to be open around pretty consistently around 3 AM EST-- that's the time I usually recommend to friends who want to make a character there.

Also, it's important to note that the page linked above is only updated every few hours and thus is often wrong about whether a world is open or closed for character creation. The only way to check for sure is to try creating a character and see whether the world is available or not at that point in time.