The ancient egyptians originally divided the day into two parts, dark and light, which is what their mythology was based on - the death of the sun god each night and his rebirth each morning. When sundials were first used, egyptian astronomers observed a set of 36 stars that divided the night sky into into equal parts. The passage of night could be marked by the appearance of 18 of these stars, three of which were assigned to each of the two twilight periods when the stars were difficult to view. The period of total darkness was marked by the remaining 12 stars, again resulting in 12 divisions of night. This gives us our basis for 12 hours of day time and 12 hours of night.

The use of 60 in time (60 seconds in a minute, 60 minutes in an hour) originated with the Babylonians, who inherited a similar, cruder version from the Sumerians. They used 60 (sexagesimal) as a basic unit in mathematics, but no one is really sure why they did this. It most likely came from the Sumerian accounting system, which was what cuneiform was first developed for. The temples were responsible for storing and distributing food. 60 is a base number that is divisible by 1, 2, 3, 4, 5, 6, 10, 12, 15, 20 and 30, and it would have been useful for calculating amounts of grains and beer in storage and then for calculating rations for the public. The same base number was eventually applied to time.

It's also worth noting that we still use these units in food and drink distribution today - we still buy a 6 pack of beer, and a pack of 12 bread rolls.