Cold. All OEM's door placards specify the tire pressure be set when the tires are "cold". But what is cold? From a random Honda owners manual:
Measure the air pressure when tires are cold. This
means the vehicle has been parked for at least three
hours, or driven less than 1 mile (1.6 km). If
necessary, add or release air until the specified
pressure is reached.
If checked when hot, tire pressure can be as much as
4–6 psi (30–40 kPa, 0.3–0.4 kgf/cm2) higher than if
checked when cold.
Note: This means ambient outside air temp, not inside a warm garage.
Low tire pressures carries far higher risk than high pressure. Since low pressure causes tire heating which leads to rapid deterioration and possible explosion. Low tires also cause poor handling due to higher flexibility in the sidewalls.
High pressure carries a shorter list of problems; The smaller and misshaped contact patch increase centerline wear and can reduce road friction.
The OEM's want the pressure on the higher end of the allowed range because of the lower risk and the pressure is going to drop naturally.