The Causality Dwell Bound: Minimum Transit Time for Displacement Through a Fifth Coordinate

A transit that changes ordinary position as well as phase invites an immediate causality question: what stops the effective speed from exceeding the speed of light? This paper derives the answer as a minimum dwell time. If the phase advance itself takes dt_phase = 3.291e-16 s (the energy-time floor at 1 eV), causality requires total elapsed time of at least Dx/c for ordinary displacement Dx, so the transit must include a dwell of at least Dx/c minus dt_phase. For 1 km the minimum dwell is 3.336e-06 s; for the Earth-Moon distance the light time is 1.2822 s and for one astronomical unit 499.0 s, in both cases essentially the whole journey. Omitting the dwell for a one-metre laboratory displacement would imply an apparent speed of 1.014e+07 c. The transit law is therefore compatible with relativity only in its dwell-inclusive form; instantaneous displacement is excluded at every distance. Computed; not measured. SIMULATED, NOT MEASURED.