Charlotte and Seattle are about 2,281 miles apart by road. Split the difference and you arrive near Denver, the city closest to the halfway point between them. That puts roughly 28 hr 26 min of driving on the Charlotte side and 21 hr 23 min on the Seattle side — the fairest single meeting point among the cities near the middle.
Over this distance most people will fly rather than drive the whole way. Denver still makes a fair, central place for Charlotte and Seattle to converge, splitting the travel instead of asking one side to cross the country.
If Denver doesn't have what you're after, Omaha and Kansas City are also close to the midpoint and worth a look — each keeps the drive reasonably balanced between Charlotte and Seattle.
City descriptions adapted from Wikipedia (CC BY-SA); photos via Wikimedia Commons, credited above.