When you're editing multiple campaigns with the Bulk Edit Day Parting dialog, you choose which hours and days the campaigns can bid on impressions.
When you click Save, the day parting rules you set override any rules that had been previously set in the chosen campaigns.
If you want the campaigns to run past midnight, set two rules, one that covers the hours before midnight and one that covers the hours after midnight. For example, to run a campaign from 11:00pm to 4:00am every night, you set these two rules:
If you select Use local times, dayparting takes place in the users' time zones. Otherwise, the hours represent Eastern Time, and daylight saving time is observed.
For example, if you are running a nationally (US) targeted breakfast campaign that is only supposed to run from 6:00am to 9:00am, then Use Local Times ensures that the ads are seen from 6:00am to 8:59am wherever the users are, as opposed to Eastern Time. Reporting will show that there was spend from 06:00am through 11:59am, which is correct since reporting is in Eastern Time. (6:00am to 8:59am PT is 9:00am to 11:59am ET)
Campaigns that use local times cannot also use campaign-level pacing.
Disabling Day Parting
If you want the campaigns to run throughout the day, select All day in the Day Parting dropdown.