So I'm playing on PC and I can't log in, it gives me that error code and tells me the game is still under maintenance, even though maintenance has ended. I've tried quitting the game and restarting it but, still the same thing. Is this a bug or just some kinda weird delay glitch? Do I just have to wait?

Yes the game was still under maintainance when you post about this. Seems you misunderstand about maintainance period.

It said it was finished earlier, but I've just now noticed they've extended it by an hour. I guess I do have to wait after all.