On Neptune, a day is about 16 Earth hours and 6 Earth minutes long. Neptune has a much longer day than Earth due to its slow rotation, which results in a longer day-night cycle on the planet.
Actually it doesn't.
Neptune's year, or orbital period, is approximately 60,190 Earth days, which is equivalent to about 164.8 Earth years. This is due to Neptune's far distance from the Sun, resulting in a much longer orbital period compared to Earth's 365-day year.
16 Earth hours
Neptune has a shorter day than Earth, it spins once on its axis in 16 hours and 6 minutes, compared to 24 hours for Earth.
The rotation of the planet Neptune is much faster than Earth's. It completes a rotational "day" in about 16 Earth hours. So in an Earth year (365.25 Earth days), Neptune completes about 544 Neptune days. In a Neptune year, there are about 89,666 Neptune days.
Each day on Neptune takes 19.1 Earth hours. A year on Neptune takes 164.8 Earth years; it takes almost 165 Earth years for Neptune to orbit the sun once. Since Neptune was discovered in 1846, it has not yet completed a single revolution around the sun.
No two planets in our solar system have the same length of day or length of year. Compared with Earth, these planets have longer years: Mars, Jupiter, Saturn, Uranus, Neptune. These have much longer days than Earth: Mercury and Venus. Mars has a day that's slightly longer than Earth's day. Depending on the particular definition of "day" that is used, two planets have a day that's longer than than that planet's year. They are Mercury (solar day) and Venus (sidereal day).
At its equator, the rotational speed is 9660 km per hour.
Neptune's year is about 164 Earth years long.
Neptune has a longer year than Mercury. The closer to the sun a planet is, the faster the orbit and shorter the year. Neptune's orbital period (year) is a little under 165 Earth years. Mercury orbits the sun in just under 88 days.
A day on Mars is slightly longer, about 24.62 Earth hours (24 hours, 37 minutes).