Day parting allows you to specific what days and times you want to run the ad. It can be selected from the Advanced Settings option.
Once selected, choose to enable it, and then select the hours and days you wish to run on. There is an option at the top to enable the same hours for the whole week, or different selections can be made for each day. The example below could be a good selection for a sports ad, looking to target Friday night, and Saturday/Sunday afternoon sports for instance.