Maybe a bit over 12 straight hours and didn't worry about the genny working too hard although it was putting out near it's max rated wattage. Onans love to run and properly maintained will happily provide power for many thousands of hours.
We average about 100 hours per season (yearly) but that's when we are boondocking and camping in temp extremes where heating or cooling the rig via generator is required. Having all the power to run our entire RV with a flick of a switch makes for worry free camping.