This theoretical biophysics study models the radical pair mechanism as an open quantum system to derive an explicit dependence of magnetic-field effects on the spin coherence relaxation time (τ) and chemical kinetics (k). It reports a condition under which RPM effects become significant and estimates τ in cryptochrome-like proteins to be on the order of units to tens of nanoseconds. The paper also reports that nanoTesla-level radio-frequency fields have minor influence and are unlikely to disrupt RPM patterns under the modeled decoherence.