You can time a shutdown on your computer easily by creating a short vbscript that contains either only the shutdown command, or a shutdown command with an integrated second timer. If you do not add a timer, you can also use Windows' Schedule Tasks function to have the computer shutdown at a specific time. The vbscript to shutdown looks like this:
Set objShell = wscript.CreateObject("wscript.Shell")
If you want a timer, add
to the quoted expression in the second line, where x is the number of seconds to count down. Enter this code into a notepad and save the file as .vbs. Do not save it as text file.