Venus has the longest sidereal day (period of rotation or spin). This "day" is 243.0185 Earth days long and Venus rotates in the opposite direction of Earth. This day on Venus is actually longer than its "year". It takes more time for the planet to turn one time on its axis than it takes to go around the Sun. A "year" on Venus takes only 224.7 Earth days.
However, the longest solar day occurs on Mercury, which completes its slow spin about once every 59 Earth days but also circles the Sun in just 88 Earth days. This tidally-locked combination leads to a solar day (roughly sunrise to sunrise) of 176 Earth days, twice as long as the "year".
On Venus, because it rotates clockwise but orbits counter-clockwise, the effect is to make a solar day ("daytime" is brighter, but there's no sunrise through the clouds) about 116.75 Earth days.
Minor comment: The actual question may be asking something different, but that's not clear.
The answer is NOT Venus. It is MERCURY. Venus takes longer to spin once than does Mercury. However Venus spins in the opposite direction to Mercury. The result is that Mercury has the longest "sunrise to sunrise" times.
As can be observed on any sunny day, the shadows are longest at sunrise and at sunset.
The sun casts the longest shadows immediately after sunrise and immediately before sunset.
Uranus has the longest day of any planet in the solar system, with a rotation period of about 17 hours and 14 minutes.
Just after sunrise, or just before sunset.
Mercury has a double sunrise.
when its its sunrise and evening.
The longest day of the year in the northern hemisphere is during summer solstice. Th longest day in the year for the southern hemisphere is during winter solstice.
The length of a day on a planet would determine how long you sleep. Venus has the longest day in our solar system, lasting about 243 Earth days. So, if you were to live on Venus, you would have a much longer day to sleep through than on other planets.
The planet is Mercury. (Some people think it is Venus, but it is Mercury.)
because the sun isn't there
Jupiter is the largest with the largest diameter.