All time semantics are culturally relative. There is no one, correct way of observing time. In Risk: A Sociological Theory, Luhmann wrote,
[Just] as binocular vision produces spatial depth for the purpose of resolving self-produced visual inconsistencies, the even more complex memory generates temporal depth in the twin horizons of the past and the future. Although everything that happens does so simultaneously, memory-aided operations cannot take everything that they examine as being simultaneous, for this would lead to unbearable overlapping, to confusion, to inconsistency, and to disorientation. With memory the system is thus in a position to provide itself with temporal distinctions for the purpose of bringing order to the self-generated disorder. The ‘before’ and the ‘after’ of an event become discrete, and complex systems finally become capable of seeing the future in the mirror of the past and of orienting themselves by the difference between the past and the future. (p.36, italics added)
For modern, functionally differentiated society, the past/future distinction overrules the time/eternity distinction, as well as other temporal distinctions like duration/transience. If we wish to pursue a digital theory, we can reenter a prior distinction rather than positing a third value.
The older distinctions are analog rather than digital distinctions. Time/eternity and transcience/duration are not mutually exclusive, or true distinctions. A digital distinction (past/future) was needed to deal with increased social complexity produced by the (15th century) invention of the printing press and the rapid spread of literacy, as well as functional differentiation where different time horizons came into play. For instance, the legal system and the mass media systems operate with very different senses of time.
Books served as a new memory technology. Thus, the horizon of the past was greatly extended. The horizon of the future extends as far we can imagine; however, where the future is concerned, all most of us care really about are the possible consequences of our decisions or others’ decisions. From this it follows that “modern society represents the future as risk” (Risk, p. 37).
But what of the present? Luhmann argues that the old tripartite division of past, present, and future causes confusion because it’s based on a metaphor of the movement or flow of time. Past/present/future is also nondigital. It’s a continuum.
But the unity of time is not the unity of a movement; or at least we must free ourselves from this notion to the extent that it is no longer possible to describe this movement as the self-realization of the mind [Hegel], as progress, or–in the sense of pre-Darwinian evolutionary theory–in some other way as unity. We must consequently remove the present from the two-sided form form of time, from the distinction of past and future. . . . The present is to be understood as the vantage point of the observer who observes time with the aid of the distinction of past and future. For this very reason tertium non datur [the law of the excluded middle] must apply to his own observation. The present itself is –if we schematize time in this manner–the invisibility of time, the unobservability of observation. . . [The] present remains in the blind spot in this observation. (Risk, 41-42)
All semantics of time are ways of resolving the paradox of time, which is the unity of a two-side form. Everything than happens happens simultaneously. (But simultaneity itself is a produced by the distinction between simultaneity and non-simultaneity. Simultaneity/non-simultaneity is a two-sided form.)