[Method 1]
Enable the atd daemon
# /etc/init.d/atd start
Set the time
$ at 8pm
Set command, Press CTRL+D
$ at> Command
Sample format of time:
Run job at 6am on monday:
$ at 6am monday
Run job in 5 minutes time:
$ at now + 5 minutes
Run job at 4pm but 3 days later:
$ at 4pm + 3 days
Run job at 10am on 31st July:
$ at 10am Jul 31
[Method 2]
Edit /etc/crontab, and set the time
In this example, the command is /sbin/reboot.
0 * * * * /sbin/reboot
Reference:
http://www.cyberciti.biz/tips/howto-shutdown-linux-box-automatically.html