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What the statistics above show is that every planet orbits the sun and if you are standing on each of the planets, these are the number of days each planet would have in a year or for the time it would take for that planet to circle the sun. The statistics very clearly indicate that the planets farthest from the sun obviously have long years or revolutions around the sun so they logically have much more days. The planets closet to the sun have smaller years or less time to orbit the sun and so have proportionally fewer days per year. The relationship is rather obvious really, but please note the number of rotations or days specified here are what each planet would have if you lived on each planet, not increments of 24 hrs from earths perspective. If you were to sit on Mars and revolve one full revolution around the sun, you would experience 670 days, or rotations. So for Venus a year is 224 Earth days and it rotates 243 days so in a year Venus basically has one day if you sat on it.

It is therefore logical to conclude that if the Earth had 420 days then yes as you say the rotations would be faster, but this is not the only answer. When considering the evolutionary changes that have occurred on Earth with regards to species size and adaptive changes, then your planetary movement suggestion could be reconsidered. It is perhaps far more logical to consider the possibility that 420 days in a year could be recorded if the distance of the Earth was further from the sun and this also explains the evolutionary changes.