My driving days have run 5 to 22 hours, depending on the need to get where by when. There are diminishing returns. A five hour trip might be a full five hours of driving, at least four and a half. When it gets up to 18-22 hours, I more often lose 2-3 hours on breaks for meals and other refreshment.
A really long driving day takes some preparation, and doesn't work for consecutive days, so I might even delay the start of such a trip (or any trip longer than 10 hours) by a day to get ready, and have several times simply chosen to abandon the trip and the nearest major airport and fly to my destination (20 hour drive = 3 hour flight).
For consecutive travel days on a touring road trip, I try to limit my camp to camp time (when RVing) to 8 hours, and might be 3-6 hours actually moving. When using hotels, I might increase the length of the travel day to 10-14 hours, 8-12 of it actually moving.
Or are you asking about something else. I go at most three hours between rest breaks, sometimes two hours, but those breaks will be 5-15 minutes. When pushing my driving day beyond 10 hours, one of those breaks might include a 30 minute nap.
In case talking about hotels/motels raises a question of relevance, when going for maximum distance in minimum time, I do sometimes park the RV and stay at a hotel, it saves about two hours compared to going in and out of a campground. One could also Wallydock. Long trips abandoned to air travel, none of those were RV, rather for medical care (where comfort of patient during travel can matter) to get someplace for a family event like a funeral (six in the last four years).
Tom Test
Itasca Spirit 29B