physics to the rescue!
With the common form of ideal gas law: PV=nRT
Albeit, your volume will change since air is permeable [a standard unit of permeability is called the Barrer] for this discussion, let's say it's the same, as the time constraint being so short, the impact is negligible. So with volume, number of moles and the gas constant being the same, you get P1/T1=P2/T2.
35PSI = 2.41316505e+5pa, with a variation of 15°, you should have a reading of 2.2806e+5pa, which is about 33PSI¸
I think it safe to assume that your sensor is approximating it to the lower value.
And whatever gas your using, it as no impact, the same will happen with nitrogen, but to a lesser degree. In fact, there's many compelling reasons to use nitrogen, but that's not on them. As the N molecule is a tad bigger than O, it is a bit less permeable. At 25°C, O2 is about 10 Barrer and for N2 is about 3. Keeping in mind that air is 78 percent nitrogen, just under 21 percent oxygen, and the rest is water vapour, CO2 and small concentrations of noble gases such as neon and argon. In order to benefit the good stuff of nitrogen (less permeable, tire pressures will remain more constant, less moisture inside your tires meaning less corrosion on your wheels) you should be using 95% pure N2, if not 100% pure.
