Given the function of the law is to stabilize normative expectations, time is the most relevant dimension.
In an article titled “Luhmann: Law, Justice, and Time,” Richard Nobles & David Schiff (2013) wrote:
Time is central to Luhmann’s writings on social systems. Social systems, as systems of meaning, operate within three dimensions: factual, social and temporal. Each of these dimensions entails selections of actualities from potentialities (or contingencies) within horizons. Whilst the factual dimension involves selections based on distinguishing ‘this’ from ‘something else’, and the social distinguishes between alter and ego (asking with respect to any meaning whether another experiences it as I do), the temporal dimension operates with the primary distinction of before and after. In the temporal dimension, everything is ‘ordered only according to the when and not to the who/what/where/how of experience and action’ (Luhmann in Social Systems Social. Stanford University Press, Stanford, 1995, p. 78).
More on time: Luhmann wrote,
Only observations of the second order provide ground for including contingency in meaning [or sense] and perhaps reflecting it conceptually. Observations of the second order are observations of observations. This can include observations of other observers or observations of different observers at different points in time. Depending on these variants, social and temporal dimensions can be distinguished in the production of meaning. This makes it possible to state that contingency is a form that takes on the factual dimension of the medium of meaning, whereas the social dimension and the temporal dimension pull observations apart.” (“Contingency as Modern Society’s Defining Attribute”).