METHOD # 1

Right click on your desktop and choose "New=>shortcuts".
In the box that says "Type the location of the shortcut",
type in "shutdown -s -t 3600" without the quotation marks and click next. Note: 3600 are the amount of seconds before your computer shuts down. So , 60secs*60mins=3600secs.

Make up a name for the shortcut and you're done.
You can change the icon by right clicking=>properities=>change icon=>browse

TO ABORT:
To make an abort key to stop the shutdown timer just create another shortcut and make
the "location of the shortcut" to " shutdown -a" without the quotes.

METHOD # 2

EASIER THAN THE PREVIOUS ONE}
Here is another trick to shutdown at a specific time, for example you wish to shutdown at 11:35am. Type this in
start=>Run
Type Code: at 11:35 shutdown -s
TO ABORT:
Code: shutdown -a