If you ever need to schedule shutdown Cool Shutdown is piece of software you need. It is very simple - does only what it has to do.

You can select between two modes: "Turn off after specified time" and "Turn off at specified time". For example, if you select first mode and enter "00:05:10" your computer will shut down after 5 minutes and 10 seconds, but if you select second mode your computer will shut down at 00:05:20 AM.