The whole idea seems pretty unlikely to me. The ratio of the length of the day versus the night has not changed, and I don't see any reasonable biological expla

The whole idea seems pretty unlikely to me. The ratio of the length of the day versus the night has not changed, and I don't see any reasonable biological explanation for a process that is possible only when the days are long. The most reasonable explanation is simply evolution. More efficient microbes will grow faster and will out-compete the others. But more efficient microbes will also produce more oxygen. So even with a short day length, they would have eventually produced the oxygen.