I pay no attention to meter hours on engine oil changes, I change yearly, every spring and use a top tier oil (Rotella T6 and a Kubota filter). I send in an oil sample and it always comes back fine and Blackstone tells me I can 'run it farther' With 6000 and 3000 hours on the tractors and no issues, I'd say all is good. Just because the oil is dark don't mean it's shot. What that really means is the additive package is doing it's job, keeping the contaminants (by products of combustion) in suspension and keeping the insides clean. I probably run 500 Plus hours yearly on each of them, sometimes more, sometimes less.
Engine oil and hydraulic oil and filters are the cheapest consumable items any tractor has. Do the same with my vehicles but I also add a nano-borate additive to the diesels.