Structural Time Theory (STT) is presented here as a conceptual framework for reinterpreting the relation between proper time, gravity, and causal structure. Rather than proposing a new empirical modification of General Relativity or a model aimed at resolving specific cosmological anomalies, this work explores the possibility that gravity and temporal evolution may be understood as distinct operational readings of an underlying causal organization. The central concept introduced is causal-ordering density: an effective property associated with the degree of causal structuring among events. In this formulation, the scalar field τ is not identified with causal density itself, but is used as a mathematical index of a causal foliation. A minimal cuscuton-like non-propagating sector is adopted as a covariant formal anchor. Its role is not to introduce a new particle, force, or physical substance, but to provide a controlled way of indexing causal organization while preserving local operational physics. The work emphasizes the distinction between the conceptual hypothesis and its mathematical representation. It should therefore be understood as a foundational and interpretative proposal rather than a complete replacement for General Relativity, a full cosmological model, or a quantum theory of gravity. Keywords: structural time, causal density, proper time, gravity, causal structure, foliation, general relativity, cuscuton.