Even in ultralow quantities, oxygen vacancies (V O ) drastically impact key properties of metal oxide semiconductors, such as charge transport, surface adsorption, and reactivity, playing central roles in functional materials performance. Current methods used to investigate V O often rely on specialized instrumentation under far from ideal reaction conditions. Hence, the influence of V O generated in situ during catalytic processes has yet to be probed. In this work, we assess in situ extrinsic surface V O formation and lifetime under photocatalytic conditions which we compare to photocatalytic performance. We show for the first time that lifetimes of in situ generated atomic V O play more significant roles in catalysis than their concentration, with strong correlations between longer-lived V O and higher photocatalytic activity. Our results indicate that enhanced photocatalytic efficiency correlates with goldilocks V O concentrations, where V O densities must be just right to encourage carrier transport while avoiding charge carrier trapping.