The secret is not staying in your vehicle for long periods of time. The problem with not all, but some of the carriers is that they will drag their deliveries out throughout the day so they get back to the post office just prior to clocking out. That means parking your truck, and sitting in it to pass the time. If you get back too early, they'll put you to work sorting mail, or doing other stuff. We used to have a carrier who parked his truck, and visited somebody in the building across the way. He'd be there for hours. The guy we have now is a sweetheart, and he puts up with my package deliveries without complaint. I live on the third floor, and I can count on him to bring my packages up to my door, and he'll even knock on the door to let me know he's got something for me. The subs who cover for him on his days off, end up delivering packages from another building to me, or leave my packages in the front hall, which bugs the crap out of me, because I don't go downstairs every day to get my mail out of my mailbox.
Times have changed. I can tell you that any carrier staying in one spot more than 10 minutes will show up on a report. Had one carrier be stuck at the railroad crossing for 18 minutes by a stopped train. There was no way for her to turn around and no close route to deviate to if she could turn around. She called me to let me know what was going on. I called my postmaster to give him a heads up. Next day I get a nasty gram wanting to know what I was going to do about it. My suggestion was for them to call the railroad and discuss it with them.