Refer the answer for this question How strong and "hot" is the wind on the payload after the fairing is deployed at ~110km?
It is clear that the fairings are separated when the free molecular aero-thermal flux is less than 1135 W/m2, which usually happens at an altitude of around 110 km.
If the separation is event based, how are they measuring the flux? Else, the separation is timed for the altitudes?