The fair place to meet is Las Vegas, NV — the city closest to the midpoint of Boise and Tucson. From the farther side that’s about 10 hr 51 min of driving.
Recommended midpoint
Las Vegas, NV
From Boise
10 hr 51 min
517 mi to Las Vegas
From Tucson
7 hr 35 min
362 mi to Las Vegas
Tucson has the shorter trip; the split is off by about 3 hr 16 min. The alternatives below can even it out. Boise and Tucson are about 837 miles apart.
Boise and Tucson are about 837 miles apart by road. Split the difference and you arrive near Las Vegas, the city closest to the halfway point between them. That puts roughly 10 hr 51 min of driving on the Boise side and 7 hr 35 min on the Tucson 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. Las Vegas still makes a fair, central place for Boise and Tucson to converge, splitting the travel instead of asking one side to cross the country.
If Las Vegas doesn't have what you're after, Salt Lake City and Phoenix are also close to the midpoint and worth a look — each keeps the drive reasonably balanced between Boise and Tucson.
Las Vegas, colloquially shortened to Vegas, is the most populous city in the U.S. state of Nevada and the county seat of Clark County. It is the 24th-most populous city in the United States, with 641,903 residents 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 →
Tucson is the county seat of and the most populated city in Pima County, Arizona, United States. 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.