Personally I think 200 hours is too long depending on the amount of fluid the tractor holds. But if in doubt have a fluid analysis done. For $10 it is a no brainer for me.
I agree kuboman. I don't expect that much (if any) metal the next time I do a hydro change. It has 101 hrs. right now,and I don't think I'll wait 'till 200. I'll feel better changing it at 150.