Four roads do most of the work: I-65 south, I-24 southeast, I-40 east and west, and I-840 around the outside. Which one you’ll live on matters more than how many miles you are from downtown.
Distance to Nashville is also the wrong measurement for a lot of households. Plenty of people here rarely go downtown — their real driving is to an office park, a hospital, a school, a gym and a grocery store, and those can all sit on the same side of town or be scattered across three counties.
Don’t choose a town because Google Maps says it’s X miles from Nashville. Decide where you’ll actually need to be on a Tuesday morning.
I won’t quote you a fixed drive time, because traffic patterns here change with construction, growth and the hour of the day. Drive your route at the time you’d really be driving it — that number is the only honest one.