Install EasyShutdown on ubuntu 11.04(Natty)
Download deb package from here and you can install by double click on downloaded package
Using command line
You can also shutdown your ubuntu system at specific time using command line
Go to Applications >> Accessories >> Terminal or (Ctrl+Alt+ t) .
Enter sudo shutdown -h +m OR Enter sudo shutdown –h hh:mm.
Enter your password.
The system will then shut down within the minutes or at the time specified. Shutdown is a GUI program for scheduling a time to shutdown the system. You also have other options to shutdown and halt your running system through time.
-r Requests that the system be rebooted after it has been brought down.
-h Requests that the system be either halted or powered off after it has been brought down.
-H Requests that the system be halted after it has been brought down.
-P Requests that the system be powered off after it has been brought down.
-c Cancels a running shutdown.
-k Only send out the warning messages and disable logins, do not actually bring the system down.