Will Next-Generation Atomic Clocks Test the Universality of Time?

Quantum Electrodynamics (QED) is one of the most precisely tested theories in physics, yet its operator structure and the universality of time are introduced axiomatically rather than derived. This work examines how strongly the formal structure of QED constrains any possible underlying substrate, assuming QED itself remains exact within its domain of validity. We show that the Dirac algebra, the existence of spin-1/2 representations, and the absence of preferred internal directions severely restrict admissible underlying geometries. Under these constraints, a minimal discrete tetrahedral structure emerges as a unique candidate capable of reproducing the Dirac operator algebra without introducing additional degrees of freedom. Within this perspective, standard QED observables act as precision probes that over-constrain combinations of internal response parameters while remaining blind to the geometry itself. Time is interpreted as an effective observable arising from the projection of internal dynamical modes, rather than as a fundamental parameter. While this interpretation leaves both QED and General Relativity formally unchanged, it implies that the operational universality of time may be approximate rather than exact. We argue that next-generation atomic clocks, by comparing fundamentally different internal transitions within the same atom under identical gravitational conditions, provide a realistic and strictly differential test of this assumption. An explicit tetrahedral realization of the framework is presented as a concrete and falsifiable example. Both positive and null experimental outcomes are shown to have clear physical implications, either reinforcing the universality of time or indicating the presence of a deeper geometric structure underlying QED.