The J-31 won't come in such a short period of time. Let's be generous and say that AVIC is expediting the land-based program (for Pakistan, Egypt, Iraq, Algeria, and others). Even in that scenario, the J-31 must undergo a series of developmental steps, such as prototype testing, LRIP, weapons integration, etc. This will, at best, finish around 2030.
Next, I don't think the PAF would be the only launch customer. The promise of an ITAR-free NGFA is a big value proposition for AVIC, and I think the likes of Egypt, Iraq, Algeria, and others will also buy the fighter.
So, similar to the F-16, I think there'll be a gap between order and delivery - at least 2 years, IMO. Hence, the earliest the PAF can get the J-31 would be around 2032, assuming everything else in the chain succeeds.
The J-10CE was supposed to help the PAF modernize its fleet through the 2020s. It has a total of at least 80 on the roadmap, but fiscal constraints will slow that program too.