I ask a friend of mine who owns a 2007 mule. He said he kinda ran into the same thing you did, two saying different things. So he said he changed his at 10 hours, and then again at 50 hrs., and then again every 100 hrs. of use. Being on the safe side, you can never change one really to early. Being that you have a big investment. It don't hurt to spend a little extra $$$ on preventative maintance. He uses his on the farms.
I don't own a mule, but a diesel RTV >>>> My dealer and Kubota Mechanics Shop Book said change at the first 50 hours. Then again at 100 hours. And from then on, change ever 100 hours ..... Total cost of oil and filter isn't but $20.32 >>>>>> For that amount, a person can afford to do it more often !!!!