Metric Clock

Why is a day divided into 24 parts? Why is the basic group of days a week of 7 days? The answers are lost in the past. Ancient Sumerians and Egyptians divided their sundials into 12 parts, but I have been unable to determine why they did this. There is biblical rational for making 7 days a basic unit of days, but I am not a Christian and I don't use base 7 counting.

Here is a clock based on dividing the day into parts based on the base 10 number system. A full date is expressed as day of year plus decimal fraction of the day. For example April 3 is the 93rd day of the year. 8am is one third of the way through the day, so the full date and time would be 93.33333