There are many utilities out there that were especially tailored to help you schedule various power actions for your system, but in case you're looking for a really simple way to promptly close the PC, meet Timed Shutdown.
Incredibly lightweight and easy to use
Just like its name suggests, this tiny tool is meant to set the PC to turn off with a just a couple of clicks. The interface is just minimal and includes some predefined times to schedule a shutdown, such as right now, in 15 or 30 minutes, in 1 or 2 hours.
Set the desired time to trigger
You can also manually specify the power off time, press 'Enter' and you're all set. The great thing about Timed Shutdown is that it supports the 24-hour format for setting the closing time as accurately as possible.
Straightforward without advanced features
Since the application has been developed to be extremely easy to use, it lacks features a user would need when working with this kind of tool. You can only schedule a shutdown, so there's no option to create a timed reboot, standby, hibernate or logoff.
Limited functions overall
As soon as you set a timed shutdown, you have no option to cancel it. There's only one thing you can do to to stop the action and that is quitting the app altogether. Right-clicking on the System Tray icon gives only the possibility to exit the program.
A few last words
To sum things up, Timed Shutdown could be a decent solution for users seeking a truly simple, very basic application to do only one task: set the exact time you want the system to close. It can mostly shine on a lazy weekend when you don't know whether you get to see the end of a movie or fall asleep halfway through.