Abstract
<jats:p>Canonical quantum gravity has no external time parameter, so the choice of a physical clock becomes part of the dynamics rather than a background assumption. Prior relational, dust, geometric and scalar-clock constructions show how internal time can work in special regimes, but they leave a sharper question open: can one specify a common matter-accessible clock sector in four-dimensional covariant gravity and test, within one action, its canonical consistency, dynamical monotonicity and quantum probability interpretation? This paper answers that question for the Tempon, a Lorentz-scalar clock field coupled to matter through the conformal metric \(A^{2}(\Phi)g_{\mu\nu}\). Its first-order expansion yields the trace interaction \(\Phi T\), while the full covariant action fixes the matter momentum and Hamiltonian before any reduction is made. For an explicit scalar matter model, the exact Legendre transform gives the corrected kinetic structure and the ADM constraints, and the scalar-sector bracket calculation verifies preservation of the classical first-class hypersurface-deformation algebra. The same model then supplies a clock test rather than a clock assumption. In homogeneous FLRW cosmology, an exact Tempon momentum balance separates open fixed-sign branches from turning-point solutions where monotonic relational time fails. In the reduced quantum theory, a positive-frequency homogeneous or gauge-fixed sector supports Schrödinger evolution relative to the Tempon and a conserved conditional inner product under self-adjointness and adiabaticity conditions. The resulting framework turns the clock-choice problem into a calculable viability program, with direct extensions to clock-quality measures, fifth-force searches, precision-clock comparisons and scalar gravitational-wave response.</jats:p>