Here is some interesting info from the Peregrine Fund.
Peregrine Falcons generally keep the same mate from year to year, but if one dies, the surviving bird will seek another.
A typical clutch is three to four eggs, which are incubated for 32 to 35 days. The parents will use their beaks to roll and shift the eggs periodically during incubation. The male assists by sitting on the eggs while the female leaves to eat. The eggs will not hatch if they are infertile or the young dies during incubation.
Called an eyas, a chick stays warm under its parent during the brooding period. Chicks are fed by both parents, who make sure each chick receives enough to eat. They are in the nest for six to seven weeks.
Chicks prepare to leave the nest by flapping their wings in the nest, then taking short test flights. For about six weeks, they continue to be fed by their parents while honing their flying and hunting skills before striking out on their own.
With this in mind, we might expect to see some hatchlings around 17 May to 20 May. We’ll see.