In the Hindu calendar, the kalpa is a measure of time equal to 4,320,000,000 years. (source)

The earth's rotation is slowing down. In the Late Cretaceous period, around 85 million years ago, the earth rotated so much faster than it does now that a year consisted of 370.3 days, and in the Cambrian era, around 600 million years ago, a year consisted of about 425 days. Of course, the length of the day in the past would have been shorter than it is today. (source)