Ideas:

If this type of glyph shows a period of time, and to be more specific - the period of Waning Moon - then there seems to be no correlation between the length of the glyph and the length of the time period. For there are 6 'spines' only for the Waning Moon, whereas the Waxing Moon has 7. So if the period in question refers to the number of nights the moon is visible, there is no correlation (given that my idea is correct that the period of New Moon is located in the period of the Waning Moon).

On the other hand, if the length of the glyph does not refer to the time the moon is visible, but instead to the total length of the Waning Moon, then the lengths of the two 'rectangular' glyphs should be equal (as they are).