There are actually many shutdown timer software for you to choose, but you can still schedule a computer-free shutdown with the commands in the system.
Guide Timer shutdown computer in Windows 8
Step 1 Press Windows to open Metro on Windows 8.
Step 2 Right-click anywhere to show the task
Step 3 Drag the slider to the position Run in the table of these applications.
Step 4 Dialog box Run appears you type cmd -> press Enter then table Command Prompt in the Windows 8 system appears.
Step 5 You type in that command: shutdown -s -t 500
Shutdown: general shortcut command
-S: Is the action performed (here is off -s = shutdown)
-t: The time command in Dos calculates the timer state
500: After how many seconds the test will shutdown.
The end of the command is Enter.
Step 6: Then there will be specific notifications from Windows.
Step 7: If you do not want to turn off the device at this time you can cancel the automatic shutdown by command shutdown -a ––> Press Enter.
Step 8: The system will notify you of this cancellation.
The above is an automatic shutdown timer that you can apply on Windows 8, without any software to consume machine resources and still very effective.