The shutdown command comes in handy if you want to shutdown or reboot your Mac at a specific time. Here are some of the examples. You should be a super user to use these commands.
# SYNTAX: sudo shutdown [options] when [message]
# Shutdown immediately
sudo shutdown -h now
# Reboot immediately
sudo shutdown -r now
# Shutdown at 9 pm
sudo shutdown -h 21:00
# Shutdown in 5 minutes
sudo shutdown -h +5
# Restart immediately
sudo reboot
# Shutdown immediately
sudo halt