Always, always, always use cold temperature stated on the side of your tire, Check an inflate the tires when they are cold, never, never deflate a hot tire to a cold temperature.
If you think a tire is going flat and you check it an it reads low, then inflate the tire to match the already warm/hot other tires, then check that tire again the next time you stop again, if it's low again then seek out a tire shop to get tire repaired or change to your spare if you have one ...
Only add air if the tire is going flat, temps will very on different road surfaces, cement, asphalt, hot and cold ambient temperatures. They will always gain air when hot and loose when cold unless they a filled with nitrogen an then they will still gain some or loose some but the temperature of the tire will however run cooler overall ...
I always check my tire pressure 1st thing in the morning before starting out, i check the temperatures of the tires and axle hubs during the day when I stop to make sure they are not overly hot to the touch, some people use lazier gauges to do this same thing.
Safe travels
