You can time shutdown on your computer easily by creating a short VBScript that contains either only the shutdown command or shutdown command with an integrated second timer. If you do not add a timer, you can also use Windows' Scheduled Tasks function to have the computer shut down at a specific time. The VBScript to shutdown looks like this:
Set objShell = wscript.CreateObject("wscript.Shell")
objShell.run("shutdown /s")
If you want a timer, add
/t *** to the quoted expression in the second line, where * 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 a text file. See here for other ways to shutdown Windows using a timer.