How long does it take to get to Neptune from Earth?
How long it would take to get to Neptune from Earth would depend on the path chosen and on where Neptune and Earth were in their orbits when the mission was launched.
For example, the Voyager 2 spacecraft was launched on Aug 20, 1977 and it reached Neptune on Aug 24, 1989. So, Voyager 2 took about twelve years to reach Neptune. As of the time of updating this article in January 2022, Voyager 2 is the only spacecraft to have visited Neptune.
For more information about Neptune, check out NASA's Solar System Exploration Neptune Overview webpage.