If you didn't have a set-aside control group, you wouldn't know if it was the post office that caused them not to hatch, or the method itself. Let's say we're going to ship in the month of April, and it's not a far enough distance for an airplane. Remove the variables of bad weather and cargo holds. (Does USPS even use airplanes for say Cali to NY? Or would it be a semi trailer and all the varying temps across the US?)
These are all the ways it would have to tried with control groups. Buuuut... here's the kicker... they need to be all the same eggs. For the sake of science, to remove as many unknowns as possible.
12 eggs to go as normal, the control group. They will be started when the 3 day incubated eggs are re-set, for the same hatch date. In theory.
36 eggs go in for a 3 day set. 12 of them are removed and placed at room temperature. 12 more are placed in a "warm" fridge to be around 45 degrees. The last 12 are placed into a shipping box, wrapped as normal. Room temp, that night put into the 45 degree fridge. Remove in the morning. Throw it across the room onto the couch. Simulate shipping! Warm and toss it, cool and slide it, warm and drop a book on it, cool it and throw it again. Don't beat it up, pretend you read the fragile sticker and throw it gently.
Re-set the 36 eggs and the 12 control eggs. Proceed as normal. After what, 4 days of "shipping"?
So to do it right, we would need 48 eggs from the same source. If the data is inconclusive, then we need to do it on a larger scale, with an egg chain so to speak, each person offering 36 eggs, keeping 12 for themselves to start and stop as a control group, and the rest go to two different places so that it's two groups of 12.