In my opinion, time span is as important as hours of use. If you put hundreds of hours a year on, I would go by the book. Much less, I suggest yearly, maybe every other if synthetic is used. Lots of opinions, more to follow.
For my tractor, which happens to be a 4701 but used to be a couple other models, I change once a year, oil and filter. Usually put about 70 hr a year on it, but would change even if I used it less than that. Get those acids and etc. out of the oil with some fresh stuff.