My first 6 were shipped as 17 week old started pullets. They were fine when they arrived. I believe that after being dropped off at the post office wherever they originate, they get transferred to FedEx for overnight shipping to the destination city -- at which point they may or may not be delivered to your local post office. There are times, even with day old chicks, that you have to drive a little farther to pick them up.
It may also be possible to take them directly to FedEx, but I'm not sure they're set up to be responsible for the birds at the destination point.