You should set your tire pressures for the current ambient temperatures.
For those that don't know the effect of air temp and time on tires....
You should expect that:
For every 10 degree drop in temperature, the pressure will be 1 pound less than at whatever you set them at when you did it last....
also, you should expect to lose around one pound of air per month.
SO, if you set the pressure at 50 psi while the air temp is 80 degrees F in July (the beginning), and then you add no air, and check the pressure when the temperature is 40F and in November (say mid-), the best pressure you should find would be 41 psi, if the tires are in average condition and filled with air instead of nitrogen.
50 psi - (1 lb x 5 months) - (1 lb x 4 (sections of 10 degrees)) =
50 - 5 - 4 = 41
I don't know the figures for Nitrogen, as it was not a popular option when I was taught by Michelin....back in the mid 90s (nice trip paid for by my employer at the time and Michelin).