They always send them priority.
Express would not help.
https://pe.usps.com/text/dmm300/604.htm
The Post Office will give a refund for late delivery of express mail items, with a list of exceptions. One of the exceptions:
"The shipment contained live animals and was delivered or delivery was attempted within 3 days of the date of mailing."
So Express Mail is not guaranteed to get there any sooner than Priority would, when it contains live animals (like chicks.)
If they were shipped on the evening of Tuesday the 8th, and you get a call the morning of Friday the 11th, the box might not be silent.
I've gotten quite a few boxes of chicks that spent that long in the mail and were fine.
(No guarantees, but don't give up hope yet.)