Former rural mail carrier here...if you paid for Express shipping and it didn't arrive in the stated time, you are entitled to a full refund of your shipping cost. Hope you still have all of the receipts/paperwork from your box. File for your refund!
P.S. The chicks are definitely alien-ish, but in a good way!
The USPS changed the rules on lives this past year. They have until 3 pm on the second day to deliver now. This was done because birds get bumped from flights where they are already carrying dry ice, because it is carbon dioxide and will kill them.