you can set them to 0.15 mm cold,
I set mine that way but run the engine up to temp and double check them hot, but it does give you a starting point
When you do your valve clearance check hot at 0.25 mm, have you found that you have to adjust the clearance at all?
I always find an adjustment necessary on at least half of them; but that's probably down to my error or temperature changes, as mentioned. Haven't tried Nickburt's method yet. So will try that next time I do mine. Also, first running after adjustment, mine runs not quite right for say 50 miles; but then settles in nice with better power and better mileage(back to normal)- then just before adjustment. In my mind anyway.