If you keep your speed on Interstates or major highways around 60-65 mph, a good estimate would be that over a day's drive, you'll average about 50 mph, which will include fuel, food and rest stops.
We live in the Los Angeles area and any trip that takes us east or northeast leaves us with very few places to stop unless we do 400 plus miles. SO our first day is always a long drive which isn't so bad when you're fresh.
When working, we often did 500+ miles a day to make it to our boating/camping destination so we had a full week of boating.
Now that we're older/retired, 350 miles is about 7 hours of driving. We did Los Angeles to Washington D.C last year and averaged about 300 miles a day.
Remember, as you get older, you need to get up and walk around more often to prevent blood clots, sore backs and legs.
Don & Mary
2014 Newmar Dutch Star - All Electric - 450 ISL
2016 GMC Canyon 4WD Crew Cab