Wouldn't released brakes expose the brake surface to air, allowing for slightly more heat dispersion than with applied brakes. It's probably a minor effect, but would theoretically let the brakes cool a little faster.
Adding to TomConard's post, the additional factor unspoken in his post is that there is the position of the thermal sensor to consider. Obviously it can't be on the business side of the brakes, and therefore it is not directly exposed to the heating. So the sensor takes time (due to the lag he describes) to actually see the brake temperature. Which means that the sensed peak may be lower than the real peak AND occur after it.