Create a text file. In the text file type "shutdown -s" without the brackets around it.
Save it as sd.bat or shutdown.bat or whatever you want as long as the extension is ".bat".
Go to >Start>Control Panel (or whatever)
In control panel look for "Scheduled Tasks"
Open Scheduled Tasks and create a new task by going >File>New>Scheduled Task
Call it whatever you want
right click on the new task you created and select properties
in the box beside "run" select the ".bat" file you created wherever you saved it.
select the "schedule" tab and then select "daily" with a start time of yourtime
Also schedule it for every day (every 1 days)
Click "advanced" beside the yourtime start time
Then select the "time" radio button beside "until". Set it to go till your time
select the security tab and hit "add"
in the text box type your username and hit enter
select your username in the box above the add button and click the check box under "Allow" and beside "Full control" to give you all the privileges to change it.
click the "advanced" button underneath.
select the "Everyone" option which should be under (or over alphabetically) your username
Uncheck the box at the bottom of the window that talks about inheritance and choose the middle option when it bitches.
click "ok" and "ok"