IMO, the USPS carrier needs a different job. Yes, I know the role has unrealistic demands and the work culture is terrible, but he's not doing his job.
A couple of years ago, I could get shipped eggs and have good hatch rates...the last 3 shipments of eggs over the past year resulted in exactly zero hatching. They tried to develop, but couldn't hatch. Air cells were terrible, and I spent a lot of time babying the eggs (upright, cutdown cartons, etc.) to no avail - the shipping destroyed them.
In short, a viable alternative to the pretty much completely dysfunctional USPS is needed. It's bad enough that "efficiencies" like automation mean that clearly-labeled boxes containing hatching eggs get tossed around by machines, but to have an employee behave like that...no.
Ok, off my soapbox now.

I hope you'll be luckier than I've been and that despite USPS's best efforts to thwart you, you still have a good hatch!