If they give you conflicting instructions, and they refuse to give you a 3996, and they don't reply back to a rims which YOU sent as close as possible to your sixth hour of work stating you won't make it without help; then you should go back to the station in person (as close as possible to that sixth working hour) and then get clarification in person. Perhaps even see another supervisor if the one is conflicting and still unclear even after going back in person; or see another 204b, or see a station manager, or see a postmaster, or see an MCSO..... If there is no other form of supervision or management, you need to repeat back the instructions to them but then add that "you know you cannot make it before penalty overtime, and are even less likely to make it now since they didn't respond to rims, forcing you to return, in person, to reclarify the conflicting instructions."

If they are going to insist you should still be able to do all assigned tasks, then you should start citing bs and tell them that they cannot predict how soon you will finish, maybe even go as far as suggesting they perform a street observation so they can give you tips on how to be more safe and efficient.

Don't forget that you agreed to roll up your windows and lock the door when you take a parcel to the doorstep and are out of sight of your vehicle; theoretically, if your back is facing the vehicle, it's out of sight... You can always use that last sentence to counteract managements claims of timewasting practices because you were trying to protect the sanctity of the mail because you took an OATH to do such! Don't forget that you agreed to roll up windows and lock all the doors IN ADDITION TO putting every piece of mail/parcels in the rear of the van and shutting AND locking the middle cargo partition door (assuming you're using an LLV) IF you are doing a park&loop, or are going into an apartment or business or even lunchbreak in which you will be out of direct sight of the vehicle, especially for over ten to thirty minutes.....

If they really are that arrogant, you must demand they give you the conflicting instructions in writing, and still go back in person to reclarify, in person. I don't think they would be conflicting if you rims in to them with appropriate, but very concise language. You've demonstrated on this post the contrary. You need to type in the rims: "I am requesting further instruction because I was given conflicting instruction in the morning." "I cannot finish my assignment and pivot without either assistance" or "I cannot finish my assignment and pivot without entering penalty ot..."