How long is an Earth day on planet Venus?

This question is meaningless. An Earth day would be the same length no matter what planet you are on. An Earth day would be the equivalent of 0.004 Venus days and about the same number of Venus year (it takes a whole year for Venus to go round its orbit). A Venus day is 243 Earth days.

That's 243 Earth days to rotate once. Astronomers call this a sidereal day.

However there is also the solar day of 117 Earth days.