IMHO you can go WAY beyond 50 hours if the engine is in good shape and you have a filter. 50 hours could easily be once a week on a long trip!
If you are not getting water in the oil, not getting gas in the oil, filtering the oil, not running the oil so cold moisture doesn't boil off, and not running so hot the oil breaks down I would let it run 100 hours.
After 50 hours my oil looks brand new, YMMV. One of my earlier A4s did the oil in very quickly from blowby and water
* you can use an IR gun on the oil filter if you don't have an oil temperature gauge. You want it probably between about 160 and 220 F.