Paper Q5b leaves the temporal coefficient A_ of the effective co-metric g^ = diag (-A_, 2, 2, 2) as the sole remaining free parameter of the Cosmochrony spectral geometry programme (open problem Q5b-O3). The present paper closes this problem by proving A_ = 2 under the Q5a hypotheses and the spectral universality hypothesis U. The argument proceeds in three steps. First, we establish a cascade internalization lemma: the temporal coordinate, identified with the BFS depth index n in Q5b Remark 3. 3, has _ as the continuum limit of the cascade increment operator T c (n) c (n+1) by the Carnot--Carath\'eodory convergence of Q5b Theorem 3. 2 (Pansu). This identification requires no new hypothesis. Second, the O-series spectral universality U, proved in U1, implies that T is asymptotically SU (2) -equivariant, so _ acts on Sym² (V_) without introducing any new irreducible representation. Third, Schur's lemma forces the unique SU (2) -invariant quadratic form on Sym² (V_) to be proportional to the Casimir Cₒₔ (₂) = 2, and Q8 fixes the normalisation scalar to unity. The effective co-metric is therefore uniquely determined: g^ = 2\, ^. No free parameter remains. The temporal direction is not an additional geometric axis; it is the continuum infinitesimalisation of the admissible cascade itself.
Jerome Beaurepaire (Sat,) studied this question.