There's no fixed time but you do sign a document stating that you intend to settle in AB. I do believe you have to at least land there but if you left right away and AINP found out, they could theoretically go to CIC and say that you lied on your application because you obviously did not intend to settle there because you did not even attempt it. They could ask CIC to cancel your PR.
As far as I know, this has never happened. It could have happened although I've never heard about it or it might happen in the future, who knows. To play it safe, you should stay in AB for a while and look for jobs so at least if somebody ever comes back to you and says you did not intend to settle in AB, you can say that you did attempt it but could not find a job.
