The pre-enzymatic emergence of metabolic cofactors remains a central open problem inorigin-of-life chemistry. Flavin cofactors (FMN/FAD) are chemically complex, redox-active, andevolutionarily universal, yet no single enzyme-free synthesis pathway is known to be uniquelyfavoured under equilibrium or yield-based reasoning. Here we show that temporal ordering aloneis sufficient to resolve this ambiguity.Using Accessibility–Ordering Invariance (AOI), we treat environmental cycling—such as ul-traviolet irradiation, hydration, adsorption, and shelter—not as background conditions but asordered accessibility windows that act as control variables. We construct an explicit and finiteflavin reaction web incorporating canonical wet-gated steps, photochemical activation channels,and realistic photolysis sinks. Route scoring under AOI reveals that ordering collapses thisspace to a single dominant backbone across exposed, sheltered, and seasonally cycled planetaryenvironments.The selected backbone is characterised by ultraviolet-first activation followed by immediatewet-phase capture via transient excited or radical flavin intermediates. Purely wet-gated routesare ordering-neutral, while stable photoaddition products are consistently secondary and sup-pressed once sinks are included. Competition analysis shows that the radical-mediated backboneremains dominant across parameter sweeps, indicating a robust ordering selection rather thanfine-tuned kinetics.These results imply that flavin cofactors could emerge without enzymes through environ-mental ordering alone, with the environment itself acting as a sequencing agent. The analysisyields a direct experimental prediction: under identical total ultraviolet dose and hydration time,UV→wet ordering must produce measurably different flavin-family outcomes than wet→UV or-dering. Full route enumeration, sink competition, and robustness analyses are provided in theSupplementary Information and the public GQR repository [1, 2].