Nathan Young wrote in
:

Further, I don't notice my oil turning black until many hours after
the change. (Lyc O-360 using Aeroshell 15W50), and I never flush the
cooler during a change.

For what it's worth.....

I have never had oil discolored significantly before 5 hours running time.
Right around 10 hours does the oil start to look like used oil in my
Lycoming AK4 360 engine.

Allen