Why No AM Postmarks On Outgoing Mail?

Factual Questions
1

Maybe some postal workers could help me with this one. It seems that just about any mail that gets sorted through a sectional center bears the “PM” as opposed to “AM” designation on the postmark. I live in a city with a sectional center, and even if I drop outgoing mail in the slot at 7 a.m. even at the facility itself, it does not get cancelled until PM. I have heard that most sectional facilities sort outgoing mail only in the PM. Why is this? Tis sounds like it would delay outgoing mail.

To me, the system needs to change. If, for example, the truck that drops off the day’s incoming mail at a branch office around 6 a.m. took back outgoing mail that was dropped off at the branch the previous evening – and then a morning shift was available at the sectional facility to cancel it at say, 10 a.m. and then dispatch it … such mail conceivably could make one of that day’s later flights to the destination city, where it could be sorted and delivered the very next day.

Is this not done for cost reasons, or does the Postal Service have their own rationale for non-AM postings?

2

PM can be as early as noon. So if they do a sort at noon and and at 6 PM, that’s only a 5 hour delay maximum from the time it was dropped off (assuming they’re open from 7 AM to 5 PM). But they’re both PM. Sure, adding a few more sorts would decrease that time, but it’s not like the Post Office is guaranteeing delivery time or anything.

3

As a rural carrier, I can answer part of the question.
I get to the office as early as 6:30 am. All the incoming mail for the day is already there. Mostly mail moves at night. The mail that moves during the day is only from the “main” post office in the area to the smaller offices. I have left the office as late as 7:00pm and no mail has come in yet. Most of the in and out happens late at night and early am.
Thus, am or pm designations are unimportant because your outgoing letter, deposited at 7am is still there at 6pm waiting for a truck.