I plan to follow my manual to a tee with oil changes, not less often, and not more often, than recommended. We all got used to changing the oil on our car every 3,000 miles. Then they improved both oil and the way engines used oil so that many cars (including mine) recommend oil changes every 10,000 miles. I will change the oil on mine about every 5,000 to 6,000 miles, but if it goes to 7,000 I won't worry about it. Of course, I check my oil on my car every couple of weeks, and if it starts to look pretty dark, I'll change it sooner.
So, with the tractor, I check the oil every couple of hours of running time. So far, with 36 hours on it, it is just beginning to degrade. I think I'll be fine until 50. I also assume that the oil will degrade quicker during its break-in period than it will down the road (for a while). I think my manual states an oil change at 50, 100, and then every 100 hours. I've already got the oil and filters for the first two, so I should be good for this year and a good chunk of next year.