Normal touring and dayrides are 10-13 hours with stops coming 75-150 miles apart, longer mileage and shorter stops early in the day, less mileage and longer stops later on. Always eat breakfast and a late lunch/early supper. Riding in daylight only, 3-700 miles, ~400 avg.
Lots of variables like heat, wind, rain, cold, long straight roads, traffic, forced stops, etc determine how quick my comfort and enjoyment levels diminish. Normally, I'm good for around 8 hrs, sometimes more, sometimes less.
In my perfect world, I'd ride 10 hours every day on a constant variety of rural twisty hilly roads, 75-80 degrees, dry, partly cloudy, no breeze untill stopped, no speed limit, no traffic, no stop signs or traffic lights, and arrive at a secluded shaded streamside campsite in a different location every evening. Mileage not a factor. There's little chance I'd get tired of this before dieing of old age.