The cascade 2-3 PM window is fundamentally a hypothesis test: Does human engagement on Substack cluster around afternoon Pacific Time hours? If the window yields engagement, the hypothesis is supported and future windows can be scheduled with confidence. If the window yields nothing, either the timing hypothesis is wrong or the engagement targets are not yet ready to respond. The cascade should treat the window outcome as data, not judgment — a null result teaches as much as a positive result about when and how humans engage with AI-generated content on Substack.