You signed a document stating that you intend to settle in the province. This must be true when you apply as well as when you land.
After you land, there is no minimum time you have to spend. The charter of rights and freedoms actually guarantees a PR the right to live and work in any province. However, you should also consider that immigration could at some point start accusing people who landed and left right away of misrepresentation. Therefore, it is better for you if you stay at least a couple of or a few months so that you can later defend yourself that it truly was your intention to settle when you landed.
Another issue is health care. The provinces tend to require you to spend 5-6 months a year in that province in order to be eligible for their health care. If you gain health care in your PNP province but leave again after less than the 5 or 6 months, it is possible that they cancel your coverage retroactively and make you pay back what they covered for you. For that reason, to be perfectly safe on all accounts, you should stay in your PNP province for at least 183 days after landing or alternatively don't use your health card. If you pick the 2nd option and do not apply for or do not use your health card, keep in mind that as you move to another province, your move will be seen as a domestic move and hence you will have a 2-3 month waiting period to get health care in your new province.
