When you shut down Windows 10/8.1/8, by default, you're not actually shutting it down completely, the way you did in earlier versions of Windows. Even though the menu item is called "Shut down", Windows actually does a partial hibernation, which is why the shutdown process takes so long. It does this so that it can boot to Windows faster the next time you turn on the computer.
Start up the command prompt by simply typing "cmd" (without the quotes) and hitting the ENTER key.
Type "shutdown /s /t 0" (without the quotes) in the window that appears, followed by the ENTER key.
System Uptime is the time during which a computer is functioning or able to function. You can learn Windows system uptime by using a system uptime software.