After you install an important update in Windows 8 or in Windows Server 2012, you receive a notice that you have to restart the computer in three days. If the restart does not occur in three days, the computer displays a 15-minute countdown and then automatically restarts. By default, this automatic restart is delayed if the computer is locked, and the countdown will begin the next time that you sign in to the computer.
A new feature is now available that lets you force automatic restarts to finish installing important updates, regardless of whether you are at the computer. You can change to this new restart behavior through the following new registry key value that was introduced in the April 2013 cumulative update (2822241).
Value data: 0 (default value) or 1 (force a restart)
When this registry value is set to 1, you are still notified of the upcoming automatic restart on the sign-in screen. However, at the end of the three-day period, the 15-minute counter begins even if the computer is locked. The restart also occurs even if the computer is locked.