Here are a few shutdown examples for quick reference.
Turn Server Off Immediately
shutdown -h now
Restart Immediately
shutdown -r now
Restart in 45 minutes
shutdown -r +45
Restart at next 1 am
shutdown -r +01:00
Restart at next 10pm
shutdown -r +22:00
Restart in 300 minutes
shutdown -r +300
Cancel any pending shutdowns
shutdown -c