It seems logical that an aluminum head, if that is what you have, has a faster coefficient of expansion than steel valves so lash will decrease as the head expands faster than the steel on heating. The exhaust valve will run hotter than the intake valve so you have more initial lash specified. That will be needed for times when the engine is run at full power.
If you can’t idle the engine while checking clearance then it would be reasonable to heat the engine, shut it off, pull the valve cover and check clearances soon. The difference in the cold and hot lash numbers that you provide indicate that the degree of hotness is not critical.
With no direction from the book, I would check the lash with the cam lobe opposite the follower.
Aren’t hydraulic valve lifters wonderful?