The PNP program is an extremely comprehensive and detailed check by the PNP assessing Visa Officers. It is for this reason that PNP holders generally receive PPR faster than applicants who applied under other immigration streams.
I did not go through any PNP program but my understanding is that the length of time to get back to PNP applicants is determined by 2 crucial factors:
1) Backlog of applicants
2) Comprehensive nature of the background check (ie if they find something they wish to investigate in your recent past, they can go to the applicant to request more information to clarify their understanding about the applicant's circumstances)
3) Delay between them sending requests to applicants for information and time taken by applicants to send the requested information
Time taken to get back to successful PNP applicants can vary. I have seen people being informed they were successful in just under 6 months and others being told they were successful after 2 years. It depends on the profile of each applicant.
