The narrator first states "the Venutian days are long ones: The amount of time from one sunrise to the next is about 8 Earth months," then later says "when it comes to the time it takes Mercury to spin on its own axis, the planet holds the record for being the slowest: Length of time, around 180 Earth days, about half a year." According to what he said earlier, Venus rotates slower, and is in fact the slowest rotating planet, as can be verified online.
In the opening tease of the show, the narrator repeatedly says "Mercury" while the screen shows an image of Venus, and vice versa.