The Egyptian Origin of the Gregorian Calendar

[snyders]

The number six represented the principles of time and space, in ancient Egypt. As such, anything to do with time keeping was based on the number six or its multiples. The day is 24 (6 x 4) hours. The hour is 60 minutes (6 x 10), and the minute is 60 seconds. The month was 30 days (6 x 5). The year was 12 months (6 x 2), plus a fraction. The fraction is equivalent to a bit over 5 1/4 days.

http://www.egypt-tehuti.org/articles/gregorian-calendar.html