I once found a sump on an O-360 that had 1/4+” of sludge in it. The guy would always call his mechanic to come do the oil change, so it was always changed cold. I once changed it and by the time he got to his hangar it was black. I ALWAYS change the oil after a flight so the crud that has settled out gets suspended and drains with the oil.
I always change the oil at 25-hour intervals and filter every other change. Oil analysis every time.