Cold, cold, cold, cold, cold. Check your tire pressure when the tires are cold.
That's cold, as in C-O-L-D, as in not hot, but chilly, not driven in a while, not warmed up, not heated, but cold, as in the car hasn't moved in a while.
Check out page 10-9 of your owner's manual:
WARNING: Tire pressures should be checked using an accurate pressure gauge when cold.
Check the pressures when the tires are cold. Be aware that it only takes 1 mile (1.5 km) of driving to warm up the tires sufficiently to affect the tire pressures. If it is necessary to check the tires when they are warm, you should expect the pressures to have increased. Do not let air out of warm tires in an attempt to match the recommended cold tire pressures.
Every tire manufacturer, every car manufacturer says to check tire pressure when the tires are cold.
As far as inflating to the maximum printed on the tire - don't do it! As the owner's manual states:
Always inflate your tires to the Tesla Motors recommended inflation pressure even if it is different from the maximum inflation pressure information found on the tire itself.
The number printed on the tire is the
maximum safe tire pressure for the tire (when cold). It's not the
recommended tire pressure for your vehicle, which is in your owner's manual and on the side panel of the driver's door.
Overinflation makes the ride harsher, makes it more likely that potholes and such will damage the tire, can lead to premature wear in the center of the tire. While steering will feel crisper, traction on the road will generally be reduced when the tires are overinflated. Maybe that's better than underinflation, but it's not better than proper inflation.
Of course, Tesla has given us a nice pressure readout on the VDS. While it's not super-accurate, it's a good guide to know that at least your tires aren't way under or over inflated, which is what you want to avoid.