I agree.I think that's a MYTH! I wouldn't risk letting them wait a day longer or 2 longer as the shipped eggs are already old as it is, especially if you don't even know how fresh the eggs are before they are packed up and sent out! Not worth the wait. Just my opinion. I mean, think about it, you can set the eggs in immediately and after a day or 2 they will settle down anyway..... it's not like they are forming into a fetus in a day or 2 while incubating!!
I set immediately after arrival and I can get 100% to hatch.