Windows 8 has a new scheduled maintenance feature that automatically updates software, runs security scans, and performs system diagnostics at a scheduled time. By default, the maintenance tasks run at 3am if you aren’t using your computer. If you’re using your computer at the scheduled time, Windows will wait until the computer is idle.
To customize this time, open the Action Center from the flag icon in the system tray.
You’ll find Automatic Maintenance under the Maintenance category. Click the “Change maintenance settings” link to customize its settings.