Amazon's built-in day-parting feature in Seller Central/ad console, offered as an alternative to building your own Day Parting (Amazon PPC) rules.
Budget Rules only lets you increase budget within a set time window — there's no way to decrease budget, and no way to adjust bids at all. Described as "an embarrassing excuse for a day parting tool" precisely because of this asymmetry: it can push more spend into good hours but can't pull spend back out of bad ones, and can't touch bids in either direction. This is why sellers turn to Manual Hourly Day-Parting Analysis (Pivot Table Method) or AdLabs (Automated Day-Parting Software) instead.
In practice this tool is only useful for one narrow case: boosting budget during hours already known to convert well, within a chosen start/end window. It cannot decrease budgets or bids, and has no per-hour bid control — so it can't replicate the kind of nuanced, hour-by-hour adjustment produced by Manual Hourly Day-Parting Analysis (Pivot Table Method) or AdLabs (Automated Day-Parting Software). Treat it as a blunt supplement to a real day-parting analysis, not a substitute for one.