If you want your ads to only run during certain times of the day or week, consider using ad scheduling, today's (Ad)Word of the Day.
Ad scheduling lets you control the days and times your ad campaigns appear. You may also choose an advanced mode, which allows you to raise or lower your bids for a campaign at certain times of the day.
Ad scheduling can help you better target your ads by selecting the times when you want to show ads. For example, if you offer special late night deals, you can set up an ad group to show those ads only between 10pm and 3am. You can also set different bids for different hours, so if you have better conversion rates during certain hours, you can set your bids higher to try and get more impressions and clicks during that time.

For more information, check out the article on ad scheduling in the AdWords Help Center.