That doesn't seem to have been a common practice around here. There have been multiple times when even tracked mail did not arrive because the carrier was unable to deliver all the mail they had.
This is from a friend of mine who works at the post office.
Praviously, after the public windows closed, they’d go to the back and finish sorting whatever mail was on the dock so it was ready to go out in the morning. How long it took varied greatly depending on how much came in that day (and Amazon in general has greatly increased their parcel volume). But no matter how much there was the standard was “processed and ready to go before you leave” so they tended to get a lot of overtime.
The new Postmaster General decided he’d rather have them punch out before OT hit and leave whatever did not get done on the dock. That quickly became a problem because the mail just keeps coming. If they got 90% done then the remaining 10% got added to whatever came in the next day, and so on.
The plan was to pick-up the slack with part-time temps, but they have had great difficulty in hiring and retaining them. It’s real work, and people seem to prefer sitting home and collecting their extra $600.
Reportedly the new Postmaster General is backpedaling and has gone back to the drawing board.