Good Math Exercise for Students to Calculate Length of Day a Million Years Ago Factoring Earth’s Spin Slowdown

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Since 1972 when leap seconds were begun added to the newly institutionalized atomic clock (very accurate), 27 leap seconds have been added, so considering therefore that the rate of the earth’s rotation is slowing .6 seconds/per year, how long would have been a day a million years ago when monkeys were supposedly morphing to become human, a billion years after the inception of life?