When I worked 10 hour shifts and was gone 11-12 hours I had someone let them out. I would think there are LOTS of adults that can easily go 8-10. Now that there is a dog door I've seen mine hunker down for a VERY (15+ hours) long time, but that is only occasionally. I'd say of their own free will they do not go out and pee anywhere near every 8 hours.
Somewhere long ago I read an article that that dogs do not need to pee nearly as often as humans because they only drink when they are truely thirsty and it makes sense. Many humans drink for reasons other than thirst. Caffine and alcohol delivery, being social, habit, etc.
So that probably doesn't help and I don't know anything from a medical standpoint, but my guys don not pee every 8 hours of their own free will. May depend on the dog