It's a bit tricky to say "only a night" on Neptune because its day and night cycle is much different than Earth's. Here's why:

* Neptune's Rotation: Neptune spins very quickly, completing a rotation in just about 16 hours. That means a "day" on Neptune is only 16 hours long.

* Neptune's Tilt: Neptune's axis is tilted at 28 degrees, which is similar to Earth's tilt. This tilt causes seasons, but they last for decades due to Neptune's long orbit around the sun.

* No Clear Day/Night: Because of Neptune's distance from the sun, the sun doesn't rise and set in the way we experience it on Earth. The planet receives very little sunlight, and the "day" is more of a period of very dim light, while "night" is a period of very deep darkness.

So, to answer your question: A "night" on Neptune would technically last about 8 hours (half of its 16-hour rotation), but the distinction between day and night is much less defined than on Earth.