Internal clock models dominate timing research, treating cultural variation as parametric input to universal mechanisms. Cross-cultural evidence increasingly challenges this assumption, but the theoretical stakes remain unclear. This paper argues that cultural temporal orientation constitutes rather than merely modulates musical time perception, operationally defined as producing processing signatures that persist at implicit levels despite behavioral convergence after extensive training. Evidence from cross-cultural rhythm studies, developmental perceptual narrowing, and statistical learning research supports a constrained version of this position, though the universalist alternative remains defensible. The paper proposes specific empirical criteria for adjudicating the debate and outlines a feasible experimental program for future research.