An advertiser who uses ad scheduling has a custom bid adjustment for 9 p.m. to 12 a.m. on weeknights. The normal bid is US$0.40 and the bid multiplier is -25%. How much is the advertiser bidding for that time period?
Ad Scheduling (also known as “day parting”) 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.
Read more here: https://support.google.com/partners/answer/2769671?hl=en