iOS 6 has a new feature which allows users to automatically silence incoming FaceTime calls and Notifications. When Do Not Disturb in enabled, a moon con will appear in the status bar as shown below.
You can turn on Do Not Disturb feature using the Options available as part of iPad settings.
Press the menu button on iPad then tap the settings icon.
In the Settings screen, tap the ON button next to Do Not Disturb to enable the feature.
This feature also provides a scheduled turn off option. Tap the Notifications below Do Not Disturb option and Switch ON the Scheduled Option
Using the From and To option, you can define the start and end time for the Scheduled Feature.
Using the Allow Calls From option, you can choose from whom you want to received FaceTime calls when Do Not Disturb feature is enabled. You can choose ether Everyone or Favorites or All Contacts or from No One. If you go for No One option but wish to receive when the person calls for the second time then turn on the Repeated Calls feature.