If Iran buys 40 Su-30SMs this year, they can get all delivered in less than 5 years, perhaps sooner. The same if they buy 40 J-10Cs. In fact, Iran can absorb all 40 J-10s in just 3 years, if not 4. Just having these 80 jets can put PAF on the backfoot since they do not have equally competitive aircraft.
However the pressure starts the moment contracts are signed, and not when the jets are actually received. It's because they have to begin making budget allocations to match that. For example, they will need a new air base near Gwadar, and expand their air base in Quetta with more advanced jets.
A follow-up of the 40+40 jets deals with license production of either one can put even greater pressure. Remember, our main goal is to put as much financial pressure on Pakistan as possible.
With a capable enough air force, Iran's attitude can also change a lot.