Miles I never concerned myself with much, dunno that.
When I had upright bikes and rode a lot, I would usually stop and get off the bike about every 1 - 1.5 hours. Reason was the pain in the butt, and usually numbness in the hands. Significant neck aches after ~6 hours.
After I got a recumbent bike, that time lengthened to 3-4 hours for my lone casual rides, and that can be easily pushed to 5-6 hours of riding non-stop without much discomfort. I don't experience seat discomfort until 8-10 hours of riding, and there's no hand or neck discomfort to complain of.
On the recumbent bike I use a camelback-type bladder (carried in the seat-back bag) and can carry food in the handlebar bag, so I can easily eat & drink while riding. The usual reasons I stop is sightseeing, restroom breaks or to re-apply sunscreen. Discomfort from just being on the bike is not much a factor.