What is the length of a planetary day on each planet?
Though I cannot give you information about the length of a day on every known planet — many are too far away to be reliably observed in this respect — I can tell you the length of a day on each of the planets in our solar system. The length of a day is determined by the amount of time it takes for a planet to complete a full rotation on its axis.
Mercury, the planet closest to the Sun, takes quite a long time to complete a rotation. One day on Mercury is 1,408 hours long — 58.7 Earth days! If you were to mark your calendar for a date two months from now, Mercury would experience just one day in that amount of time.
Venus is even slower in its rotation, taking 5,832 hours to complete a day! That's 243 Earth days.
Here on Earth, we experience days in the 23.9 hour rotation of our planet.
Mars has a very similar rotation speed to our own planet, taking just 25 hours to complete one day.
Jupiter is speedy, taking only 10 hours to complete a day. That's less than half of one Earth day!
Saturn, too, has a quick rotation. Days on Saturn are just 11 hours long, just under half of one Earth day.
Uranus takes 17 hours to complete a rotation, which is nearly three-quarters of an Earth day.
Neptune's days are 16 hours long, two-thirds of an Earth day!
Though Pluto is no longer considered a planet, many people still have a soft spot for the celestial body. A day on Pluto is about 153 hours long, or over 6 Earth days.