"GC flight logs contain a GPS time stamp which is the most exact time
standard readily available. So, violations of this requirement are
quite plain to see in these logs."

Unfortunately, sunset doesn't come with a GPS timestamp, so I'm afraid
this isn't as easy as you make it sound.

Yes, I know there are standard tables of sunset times, but these make
assumptions that may not be exactly correct and at a given location
actual sunset may differ from the calculated one by many minutes.
(Ask any local physicist./astronomer).

Of course, gross violations are pretty obvious, but I have operated
from a field where landing to the west is best done after the sun has
descended behind mountains, which usually occurs close to the time of
"official" sunset and is standard practice by those flying late.

Methinks all this scrutiny of flight logs is getting a bit too
intrusive and nit-picky.

Mike