Sir please this is all a myth...Keep tyres at OEM recommended pressure, regardless of season. And pressure is to be checked and maintained with cold tyres. Forget what pressure is at 50 C or after 5 hours of motorway cruising.
Follow the sticker on driver side door pillar.
If in city or on rough roads, you may decrease by 1-2 psi.
For highway, it is advised to raise pressure by 1-2 psi, but is not essential