Windows 8 apps will often raise notifications, alerting you to new emails, messages, calendar events, status updates and more. This is generally a good idea, but if you don't want them popping up when you're not working at the system, then a new Windows 8.1 feature can help.
Open the Charms bar and go to 'Settings->Change PC settings->Search and Apps->Notifications'. As before, you can selectively turn off notifications for individual apps, but a new 'Quiet Hours' option allows you to turn them off altogether for a period of time. Just turn 'Quiet Hours' on, set the 'From' and 'To' times and you're done. Unless you're using the PC, notifications will be disabled during that period.