Traveling through the entire United States and visiting all 50 United States will take around 2 to 3 months to complete the trip.
That factors in time for stops and staying overnight at hotels or motels or staying a bit longer to rest because when you're traveling by car or RV on a long road trip you'll want to rest for a few days to a week before proceeding on the road trip.
Driving everyday would get very exhausting and it would not be much of a vacation.
To drive the entire United States takes around 3,000 to 4,000 miles and sometimes even more depending on if you travel further into those states to visit instead of just zipping on through to another state.