There is no such thing as the "right number of molecules" in the tire. All that matters is the pressure difference between the inside and outside of the tire, which is what a simple tire pressure gauge measures. The pressure difference determines the contact patch area, which is what determines the performance of the tire. The physics of this is fairly simple. The only reason I can think of to adjust the pressure to a reference of 68°F is so that the TPMS won't give a false indication of too high or too low pressure.