The switching dynamics of an InSb optically bistable etalon are analyzed in terms of effective time constants which change dramatically near the switch points. Results are presented which show nanosecond switching, critical slowing down, optical biomodality, and noise filtration. The influence of noise levels on both the switching dynamics and the system stability close to switching are discussed. The InSb-CO system has the merits of being extremely stable and reproducible so that the detailed switching dynamics and statistics can be reliably assessed. In addition, it may be regarded as a model system so that the results presented here can be scaled with appropriate material time constants to other bistable systems.