There is a difference in “ideal” conditions and conditions “I deal” with. What you are talking about in those temperatures and humidity are ideal conditions. A lot of us don’t have those.
The closer you can store the eggs to those ideal conditions, the better chance you have of a good hatch. That doesn’t mean you are going to get a bad hatch if you don’t have ideal conditions, just that there is a greater chance of not getting a really good hatch. How long you store eggs and how far from ideal conditions both have an influence.
Eggs will develop if they are stored too warm. I’ve read different things but use the upper 70’s as a cut-off for me. If they are stored below the mid-70’s I don’t worry about it. I also try to not keep them for more than a week if I am very far away from ideal conditions.
If eggs are stored too cold, the embryo can die. Some are a lot tougher than others and not all magically die at a specific temperature. The further away from the ideal, the greater your chances for a problem.
Not all refrigerators are at the same temperature and there are warmer spots in the refrigerator. I certainly am not recommending you set your refrigerator temperature high enough to put your family at risk from the other stuff stored in there, but if your storage temperatures are above the mid 70’s, the refrigerator may be the best place for you to store them. Just try to determine the warmest place in it. Or get another refrigerator just for storing hatching eggs if you hatch enough to justify that. Just set the temperature controls for pretty warm.
I regularly store hatching eggs in the lower 70’s and get pretty good hatches. If I stored them in more ideal conditions I might get a little better hatch rate, but probably not much better. If I were a commercial hatchery hatching 1,000,000 chicks a week with several incubators that could hold 120,000 eggs each, a 1% or 2% difference in hatch rate would be significant. For me, a small tweak like that is not really worth the cost or effort.
Just do the best you can and it will probably be good enough.
