The definition from US Tire & Rim Association is
In real life this means before the tire has been driven one mile. It also implies that the tire has not been exposed to external warming from being in Sunlight.
We have shown that when a tire is in sunlight for as little as 30 minutes the temperature can rise by almost 40°F which will give you a higher than Ambient pressure reading.
You should wait at least 2 hours with 3 preferred after end of the day driving with the tires in full shade, to give them a chance to equalize temperature with ambient air temperature.
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