This is straight from Google:
"Ad scheduling (also known as "dayparting") lets you tell Google exactly when you want your ads to run, and more importantly -- when you do not want them to run. In addition, more advanced users can automatically modify their bids based on time-of-day and day-of-week cycles in campaign performance.
"Ad scheduling can also help you improve your ROI by ensuring that your ads run when it makes the most business sense. For instance, a local business may only want to run their ads during business hours, or an online retailer may want to boost their bids during their busier-than-normal lunchtime shopping period.
"If you wish to try this new feature, you can enable it via the Edit Campaign Settings page."
Reference link: AdWords Ad Scheduling
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