Would be interesting to study. While it's "only" 18g of coffee, a lot of that space is air, likely even once compacted. That being said, from the time of tamp (when significant contact finally occurs) to the time of water hitting the puck is short (probably less than 30 seconds for me).
An easy test would be to grind into the PF, prep and tamp, take temperature, wait 15 seconds, take temperature, wait 15 seconds, take temperature.
Although you'd be measuring the temperature of the surface of the puck which is exposed to atmo, and not the "middle"/bottom of the puck.
I have a probe thermometer for meat, but that would likely be really tough to use to nail the mid-puck temperature.