To get started with the basic method, pull up a regular Command Prompt and type in the following:
shutdown -s -t [seconds]
For example :

5 minutes: 300 seconds
30 minutes: 1,800 seconds
1 hour: 3,600 seconds
6 hours: 21,600 seconds

you have to put every in seconds by calculation it
If you miscalculate, or find you no longer need the shutdown timer, you can always cancel it by typing in:
shutdown -a