That wouldn't make any sense for FedEx/UPS though. If you get three packages in Atlanta, and the first and third are going to Los Angeles, and the second one is going to Birmingham, it makes a lot more sense to process package 1 and 3 together and probably take care of number 2 first.
That happens on the first sort.
You can't know what's going where to know to scan it in/ route it until after the first touch
They probably would do FIFO with overflow. The problem is that there’s no communication with the retailer about how long the delay would be.