The Nèijīng discusses time similarly as other philosophical texts of its day such as the Guanzi, Huainanzi, Shanghaiji, Zhuangzi, Wenzi, and Xìcí. The Nèijīng devotes less time to the cosmology of the subject compared to these other texts, which is logical considering that it is committed primarily to the subject of transmitting yinyang thought into medical strategy. In this conceptual model time is a category of water, time sequences are of heaven, and structural hierarchy of earth.
The likening of time to water provides context for the Nèijīng’s physiological model of circulation, which correlates time and circulation on the basis that both are matters of ceaseless flow [of water], liú dòng 流动, meaning to move/to flow/to circulate or exchange information. In the body, as in heaven, circulation has a path, a structure, and can never stop. These associations are stated in Língshū 81, where Huáng Dì and Qí Bó teach that the flow of the jīngluò follows specific rules that are at one with the movements of heaven. The conduit vessels, Qí Bó describes, “pass through the same units as heaven, and its setup is identical to that of the earth.”
Pass through/flow/liú dòng refers to movements through time and accord to the measurements of heaven, which are “the 28 constellations passing through 365 units.” In this model we see again the projection of cosmos as a human body and the centrality of the sun in matters of timekeeping in yinyang mechanics. Língshū Chapter 15 describes that there are 28 constellations that constitute the “circulation of heaven,” and that it takes one day for the sun to move through the celestial circle of 28. Likewise, the human body has 28 vessels through which the passage of camp and guard qi must complete a daily 50-fold daily circuit. The movements of both systems follow the same rate of transformation established by the solar cycle. One year is a complete cycle of 365 units, as there are 365 qi holes to correspond to one year. Ill-weather and health result with circadian dysrhythmia in either system.
Water as time is a function of heaven. However, water without structure and differentiation cannot be contained and will inundate a landscape. Water as structure is therefore a matter of earth, and in this the jīngluò are said to be identical to the “twelve river-streams.” Thus, Qí Bó summarizes in Língshū 81 that “camp and guard qi flow without cease. Above they correspond to the constellations, below to the numerous streams.” These streams are themselves beholden to the topography of the body’s landscape, a functional dynamic likened to the movement of water pouring into “mountain gorges and valleys.” This description is equipped in further detail in Sùwèn 58, which teaches that point functions are in part established by the movement of qi at that location: small meeting points are mountain gorges, big meeting points are valleys, and the partings in the flesh are intersections of gorges and valleys that serve as passage ways for camp and guard qi; “thus massive quantities of qi meet there.”
 Língshū p. 765
 Língshū pp. 245-247
 Língshū pp. 764-766
 Sùwèn p. 56
Unschuld, P. (2016). Huang Di nei jing ling shu: The ancient classic on needle therapy: The complete Chinese text with an annotated English translation. Oakland, CA: University of California Press.
Unschuld, P., Tessenow, H., & Zheng, J. (2011). Huang di nei jing su wen: an annotated translation of Huang Di’s inner classic – basic questions. (Vols. 1-2) Oakland, CA: University of California Press.