Standard relativistic physics remains predicated on the Einsteinian postulate that light propagates through a vacuum void as an invariant travel-velocity "photonic bullet" at c = 299,792,458 m/s, governed by E = mc^2. In this paper, we demonstrate that this framework commits a fundamental metrological error by conflating travel velocity across a void with Lattice Setup Time (L_s)--the acoustic "squash time" required to compress elastic inter-granule voids ("marshmallow gaps") in a 10^22 kg/m^3 rigid plenum before engaging the universal acoustic clutch. Under the Rigid Universal Touching Wave Structure of Matter (R.U.T. WSM) Framework, once phase-lock is established across the 1D Snooker Cue (Ethos-84 Heptad braid), energy transduction is instantaneous at Time-Zero (t = 0), and Einstein's E = mc^2 is replaced by the Universal Seesaw identity E = m*Phi. We present the complete mathematical master equation for L_s, incorporating the 13.3333 Hz universal motor heartbeat (f_motor), the 813.3333 Hz master resonant pulse (f_master), the 1/137.03612 Fine Structure Constant slip-ratio, and the 2,689.78 m Universal Gear Stride (D_stride). Finally, we detail the Fizeau 27,000 RPM discriminatory optical experiment, establishing a zero-parameter empirical threshold (t_open < L_s) where relativistic optics predicts partial re-emergence (~8.1%) while R.U.T. mechanics predicts abrupt, complete signal extinction (0.0% transmission voltage). While R.U.T. WSM already resolves foundational puzzles across physics--from quantum entanglement (IAAD) to cosmological paradoxes like the Hubble Tension--this benchmark is offered as a strict, pre-registered a priori prediction, providing independent laboratories with a decisive, black-and-white empirical arbiter for the physical mechanics of light conduction.