I think you're also assuming the volume of the tire doesn't change with the temp. I don't have any idea how much/little that is.

Yes, the volume can change a bit, and the temperature estimates are not precise. So these are estimates.

Also not that all of this is proportional. If you expect a 3 psi change from 54 deg F, it follows that a 1.5 psi change comes from 27 deg, and 6 psi comes from 108 deg.

So if as previously reported 5 psi low will set off your indicator, it takes a hell of a temp change for that to be temperature alone. Probably it means you were two or three psi low without the temp effect.

Yes, the message is still its time to check your tire pressure. (And sadly for me the light usually comes on after it snows--in messy weather. Better to check tires before the storm.)