Going back to Atlanta, the exception to that 6pm rule is WSB. From observation they usually do live hits in the 6 (even for stories that don't require them). But it's still repeated content from 4 & 5.
The logic stations give for new at 4 repeat for the remainders is "audiences stick around for quick hits and don't watch newscasts straight through or for hours". How true that is, IDK? EDIT: To WSB & WXIA's credit, from watching their evening newscasts it looks like they switch up the order of stories between shows.
I might run the TV for hours on one station if I'm doing something else, and the repeats are noticeable. A creative thing a station in my market does is a live VO/SOT at 4, half the story in a PKG at 5, and the complete PKG at 6, to give the illusion of new content and to keep people sticking around through shows. From a viewer POV I like it but I've heard reporters complain that turning the package multiple ways adds to their hefty workload.
And I get it. 4:00 newscasts often don't leave reporters enough room to make slot. This especially if your editorial meeting begins at 9:30 a.m, and you may not be out the door until after 10:00, plus travel time, editing, etc. The vo/sot at 4 method might alleviate this.
And from an employee standpoint the problem with unnecessary live shots, especially at night, is going past your shift hours.
If your shift ends at 11:35pm and your 11:00 live hit is an hour away from the station, that has you getting back past midnight which can be a bummer for work-life balance.