I changed my oil at 20-25 hours. Im a believer at getting any manufacturing contaminents out, if there is any. I change the oil in my new cars at the first 1000 miles too. With that said some people say it may be a waist of money, but its my money and peace of mind.
Im not racking up alot of hours either, I dont mow with it anymore, bought a zero turn. Im still putting 50 hours on it a year, from summer projects, but its definitely my dedicated snow removal equipment.
So my philisophy is, every fall I change oil, filters-hydro,oil,fuel,air etc on all my equipment getting ready for spring. It's the push mowers, zero turn, pressure washer even the BX. They are all ready to go no matter what mother nature brings us. Its alot easier to do maintenance when its semi-warm than freezing temps. You never know how much snow will come and the last thing I want is the service due in the middle of a blizzard.
Im a firm believer in Shell Rotella oil for diesel engines. Ive been running it in my Dodge Cummins diesel truck for 10 years now. You can get it anyware, auto parts stores, walmart, etc. Being in a cold winter climate, Ive opted to run Rotella T6 synthetic 5w40, blue bottle. Synthetic is like only $4-5 more a gallon, I splurged. Kubota filters and an extra set on hand too.
My BX25 is a BX2370 with a backhoe. Its stored in an unheated shed.
Goodluck Hedge