Remember that what you as a human being consider cold is not the same as what will cause thermal shock to an engine component. Even if your oil fill is via the head, the point inside the head where the cooler-than-the-head oil contacts is small and the difference between the oil temperature and the head temperature will not be great enough to cause thermal stresses of any significance.
In other words, the rate at which the portion of the head where the cooler oil is contacting (maybe a bearing cap or the cam) transfers heat will be low compared to how quickly that same contact point can transfer heat from the surrounding, warmer areas of the head to itself. If the rate of heat transfer is low, then the difference in thermal expansion is low, meaning almost no change in thermal stresses between different, bound or unbound components. By bound, I mean retained by bearings or anything else that would try to prevent two metals from expanding in opposing directions. By unbound, I mean internal stresses caused by a difference in thermal expansion between, say, the internals of the cam and the outside diameter, whihc could cause permanent deformation, i.e., it gets bent.
Finally, oil is not like water, which will remove heat at a much greater rate. For very hot surfaces, water will also vaporize, extracting even more heat energy due to latent heat losses. Oil will absorb heat from the engine much slower and its ability to coat surfaces will also help to distribute the heat it absorbs while being poured over the head to other portions of the head, causing even less of a thermal gradient.
So, to make a long story short, waiting 2 hours before pouring "cold" oil into your warm engine isn't necessary.
With respect to the "Fumoto drain valve" questions: Really? You're already on the internet, for crying out loud! There are many things that would require extensive searching or advanced degrees to fully understand, but searching for "Fumoto drain valve" is a 5 second chore and its purpose apparent.
