Create a batch file (call it Reboot.cmd for example) with the following content:
Shutdown /r /f
Create a Scheduled Task, where you call this Reboot.cmd, Run As a user with local administrator rights, set a Schedule, and you are done.
Note: check if the Shutdown command is available on the Windows version you are using (Cmd, Shutdown /?). For older Windows versions you may not find the Shutdown command. You can find it in the Windows Resource Kit. See http://www.robvanderwoude.com/shutdown.php for more information.