When applying Day Parting (Amazon PPC), granular hour-of-day bid adjustments are preferred over adjusting bids for an entire day or day-of-week.
Changing bids for a whole day alters placement settings for the entire day, not just the underperforming stretch of it — which can hurt organic rank. Sophie Society's Oliver holds this as a rule of thumb when configuring AdLabs (Automated Day-Parting Software) or manual day-parting rules: adjust the specific bad/good hours, not the whole day around them.
Claimed mechanism for why whole-day bid or budget changes are riskier than hour-level ones: adjusting a bid or budget for an entire day changes placement-eligibility/serving behavior across the full day, and if that shift lowers CTR, it can suppress organic rank — because Amazon's ranking weighs click-through behavior. Hour-of-day granularity avoids this because the change is scoped to specific hours rather than reshaping the whole day's placement mix. This is presented as a claim, not a demonstrated causal test.