High heat or high temp paint dries to touch within 4 hours.
But for the high temp pain to fully cure and dry it takes 24 hours for the high temp paint to fully cure and bond to the surface you painted.
So before heating up the metal you painted or starting an engine if you painted an engine with the high temp paint you should wait at least 24 hours before the paint gets heated up to allow the paint to fully cure.
If you apply heat to the metal or start the engine up too early then the high temp paint would likely come off the surface you painted.
The last time I painted an engine I waited for the full 24 hours to allow the paint to cure on the engine and I never had a problem with the paint coming off.
If you're painting an engine or other high temp product that sees heat then make sure you also use a high temp paint primer or engine paint primer to help the high temp paint bond properly to the surface.