It depends on a lot of things. Were you undergeared and they needed to gear you up first? Had you killed 12/13 before or were there other bosses to learn first? Has the guild been farming Archy for a long time or is it a recent kill (and still difficult to farm?) Have you made mistakes during your trial on the other bosses?
But yeah. Ask them how your trial is going, if there's any feedback or something you should work on before they can pass it.
But in general unless there are clear reasons (as listed above) why the trial drags on I'd personally leave after a month especially if there's no feedback.