Consider the relative positions of Venus, Earth, and Mars in their orbits about the Sun.
During what time of day is a launch location on the surface of the Earth facing toward the Sun (and therefore toward the orbit of Venus)?
During what time of day is a launch location on the surface of the Earth facing away from the Sun (and therefore toward the orbit of Mars)?
Based on this, you might expect Venus launches to occur during the daytime and Mars launches to occur at night.