In this world, everything is governed by the decimal system. We are living in a base-10 world. The decimal system covers the binary functions of a computer right down to the amount of change that you get when you buy something at a grocery store. Then, why is a standard Earth day not ten hours long?
Maybe, the Egyptians can answer this question. They were the first to set their clocks to base-12. This system was taken from the Sumerian culture. The Sumerians were not counting by the whole fingers on our hands but by the spaces between the knuckles of a hand counted by the thumb of that same hand. It totals to twelve.
The Egyptians divided the day into twelve-hour halves to measure time using this method. Actually, they used to interpret a day with ten hours of work to be added to two hours of morning and evening twilight and the twelve hours of darkness.
The Egyptians based the hours on the movement of the heavens. They tracked a series of small constellations known as `decans’ which were thirty six in number and rose consecutively over the horizon once every forty minutes. The rising of each decan marked the beginning approximately of a new hour. Even at night, tables were produced to help determine time by observing decans.
The Greeks were not happy with this system. Their astronomer, Hipparchus, synthesized the Egyptian star clock into the standardized equinoctial clock that is being used today whereby each segment of darkness and light on the Equinoxes is divided into equal length segments of twelve multiplied by two.