Most DSPs offer so-called "time parting" functionality, where you set your ads to run only during specific hours (and/or days). For example our product http://www.direct-ads.com/ or our competitor http://rtb.sitescout.com/ offer this.

Most decent independent (as in, sell their own adverts) publishers will offer this. Personally the main, or even only, use has been customers with age-rated products that they don't want to be seen before a children can be assumed to be asleep.