:P
You can figure about 1 lb air pressure for every 10 degree F change, given a cold tire and sitting overnight.
It should be noted that the recommended tire pressures are for COLD tires. That means they have been sitting overnight, but it assumes standard day conditions (i.e. sea level and 75 deg F).
If you are going to adjust your tire pressure, it is best to fill them up at local air source (unless you have your own) the night before and then "drain" them to the proper setting the next morning.
If your morning is 65F or 55F then you can subtract a pound or two from your target setting based on the above formula.
NEVER SET THE TIRE PRESSURE AT THE FILLING STATION!
They will be severly underinflated.
I have a digital pressure guage and just use the air at my local filling station to fill them up.
I am pretty sure COLD means something completely different up here than most other places :P