An educated guess would be the same time as daily reset. 10AM Eastern, feel free to convert that to whatever time zone you're in.
My suggestion would be to use the benchmark program to make characters in. You wouldn't get full access to how they look, but a decent idea. Then take the good ones from that (which can be saved and imported into the full game), and try them out there, lessening the chance of you hitting this limit again.

http://na.finalfantasyxiv.com/benchmark/