If your engine is hot and allow it to cool down to cold, ie, to your local ambient temp, the time it takes is approx the time it takes. Time it! So the engine feels much the same as ambient, perhaps a bit warmer. Now you know.
If this is inline with what the dealer 3 hours will achieve then, if held for two hours from hot it will be cooler and perhaps the valves can be only done in the last hour if cooled sufficiently. It shouldn't take an hour anyway. Under no circumstances should the valves be adjusted any earlier, otherwise the clearance to be adjusted will not be where it should be to enable corect final adjustment. Talk it over with your dealer so he knows what you you are aware of in relation to the needs of the situation.