There is no minimum requirement for how long you should stay but you do sign a document stating that you intend to settle in Alberta. My advice, stay long enough that just in case if anybody asks about it that you can say with a straight face that you made an attempt to settle and it didn't work out for you. That could be as little as having been in AB for a couple of months looking for a job and getting an offer from another province. If you already have a job in AB, see if you like it, if you don't like it, nobody will stop you from leaving.