Servers& how they work...
Full explanation, your server has reached its maximum for total population, example total say of 10,000 players. Wait times here can be much more frustrating to create a new character because you must wait until people delete their toon to free up space, which can be forever looking at you Gilgamesh, Leviathan, Moogle servers.
Then if you cant log-online, its because out of those 10,000 players, 8 thousands odd players are playing simultaneously, so you must wait till some of them log off the server so you can log in. These waits can be anywhere from 5 minutes to 5 hours.