Two operational rules for maintaining a day-parting schedule (see Day Parting (Amazon PPC)) once it's live:
Cadence — re-run the hourly analysis and adjust the schedule only once every 3-4 weeks. Changing it more often doesn't give enough data time to accumulate at the hourly level to distinguish signal from noise.
Isolation — don't change regular campaign bids in the same week that the day-parting schedule itself changes, and vice versa. Bundling both changes together makes it impossible to attribute a resulting swing in performance to the right lever. This is a narrower, day-parting-specific version of the general discipline behind 7-10 Day PPC Data-Collection Cooldown — wait for enough data and change one thing at a time before evaluating.