How many national news programmes in the US are an hour of unrepeated content?
The PBS Newshour. But you're trying to compare apples with oranges. The Scottish Six is basically the same as your standard 'local' news programmes in the US, Canada, Australia etc. Yes, Scotland is a nation, but in broadcasting terms, it's a national region, hence the comparison with local news programmes not national ones.
Can you find one where you get an hour of unrepeated state-wide, national, and international quality journalism?
Sorry, did you just ask whether I could find a national news programme in the US that covers state-wide news???
If you want to find something comparable to what the Scottish Six would be, then let me point you in a few directions.
Most hour long US local evening news bulletins, The 6pm NewsHour's on Global TV stations in Canada, Hour long CTV local news programming, The 6pm news on Seven Network and Nine Network in Australia, and this country, the closest equivalents are An La on BBC Alba, and Newyddion on S4C, but neither of those are one hour.
In those bulletins, at most, you'll find only the weather repeated. The news stories will not be repeated ala BBC News Channel.
It might help your understanding to actually watch a few of these.