For a release run in Army PRT, do you call running cadences or not?

A release run is well just that and they are not in formation and are no in a large group to make the calling of cadence's unnecessary and impractical. Cadences are called in formation runs to keep the formation together and in step.

Who is in charge of the PRT session? That person is in charge of the formation until the formation is released. At a minimum, the person in charge should keep the formation in step by cadence call, whether its a silent cadence and not actually "singing" cadence, until the formation is "released". If somebody out ranking you is telling you otherwise, comply, then ask to meet later to clarify with the reg and to tactfully explain that when you are placed in charge of PRT, you are calling cadence while the unit is in formation. If that is not acceptable to those who outrank you, then kindly offer them the opportunity to lead PT in your stead.

Well you can on the first portion of the run up to a maximum of 15 mins before the soldiers run at their pace bc a RR( Release Run ) is a combination of unit cohesion and integrity plus individual soldier ability. The formation runs for a specified amount of time no more than 15 mins together then at their own pace back to the starting point, so if it’s during that time before each soldier speeds up to run at their own pace it’s fine. It can be referenced in FM 7-22. I’m only giving knowledge based off what I read and understood not an expert.