You must turn on the “Shut down when idle” checkbox before you can set the delay for monitor power-down.

Use this slider to adjust the delay before the computer is shut down.

If you need to enter a delay that is beyond the slider’s range, option-click on the slider and then type in the value you want.

You must turn on the “Power down monitor when idle” checkbox before you can set the delay for monitor power-down.

Use this slider to adjust the delay before the monitor is powered down. 

If you need to enter a delay that is beyond the slider’s range, option-click on the slider and then type in the value you want.