The fair place to meet is Oklahoma City, OK — the city closest to the midpoint of Boise and Miami. From the farther side that’s about 25 hr 43 min of driving.
Recommended midpoint
Oklahoma City, OK
From Boise
23 hr 54 min
1,140 mi to Oklahoma City
From Miami
25 hr 43 min
1,226 mi to Oklahoma City
Boise has the shorter trip; the split is off by about 1 hr 49 min. The alternatives below can even it out. Boise and Miami are about 2,362 miles apart.
Boise and Miami are about 2,362 miles apart by road. Split the difference and you arrive near Oklahoma City, the city closest to the halfway point between them. That puts roughly 23 hr 54 min of driving on the Boise side and 25 hr 43 min on the Miami 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. Oklahoma City still makes a fair, central place for Boise and Miami to converge, splitting the travel instead of asking one side to cross the country.
If Oklahoma City doesn't have what you're after, Dallas and Austin are also close to the midpoint and worth a look — each keeps the drive reasonably balanced between Boise and Miami.
Oklahoma City, often shortened to OKC, is the capital and most populous city in the U.S. state of Oklahoma. It is the 21st-most populous U.S. city and 8th largest in the Southern United States, with a population of 681,054 at the 2020 census. Read more →
Boise is the capital and most populous city in the U.S. state of Idaho. It is the county seat of Ada County. The population of the city was 235,685 at the 2020 census. Read more →
Miami is a coastal city in the U.S. state of Florida. It is the second-most populous city proper in Florida, with a population of 442,241 at the 2020 census. Read more →
City descriptions adapted from Wikipedia (CC BY-SA); photos via Wikimedia Commons, credited above.
Estimates use straight-line distance and typical road speeds; real drive times vary with route and traffic.