Just change it when you the oil is getting too dark to see the stick when the engine and the oil are warm. Otherwise, the oil still has plenty of capacity to absorb dirt, esp with the close tolerances that modern engines are built with. Doing that test when the engine and oil are cold will look a lot dirtier because the oil will be thicker on the stick, so I always looked at it when it was warm. That’s what I did with a little Mitsubishi truck with a 2.0L 4-banger using Mobil 1 and got 300,000 miles out of it.
That did turn out to be ~ 5,000 miles, btw. Sometimes a little more if I did a lot of highway driving in the summer or a little less if it was a lot of short trips around town in the winter; but that was my gauge.
All of my stuff every 5000. Rotate tires too. Easy to watch on the odometer and I never have had an engine fail or even use oil.
Seems to match your test.