Whatever sort of iconic structure that surrounds the implimentation of calendar that a culture might have; the test of the calendar is the reliability of harvest. It is a profound test.
Before we had the symbolic ground necessary to build an observatory, what sort of timing structures might have presented most loudly? I think that, because of the phases of the moon, menstral cycles, and the tides; coupled with the approximate accuracy of a 13 month, 28 day/month year; a lunar month identifying four phases was most likely the origin of the seven day week. It probably would have evolved into a lunar calendar with solar correction as we became able to measure the solstices. And since there would have been a gender specific commitment to a lunar calendar; this might have been partly responsible for a schism between the sexes.