It lasts in perpetuity, sadly. Basically if you play on a high-pop server, then it's really not feasible to try to bring new players to the game. It sucks, and it's a crap system, and whoever designed it is an idiot, and Square Enix should change it. The system right now seriously makes it impossible to bring friends over to the game without either forcing them to wait until 3am (which most people would just give up instead), or forcing you to abandon your server, friends, Free Company and linkshells to switch to a lower pop server. IMO, if someone joins the game with a 'recruit a friend' code, they should be able to make a single character immediately on any server.