Screen Backlight Off

How do I just shut the screen light off without putting the system to sleep or suspending?

Does “blank screen” do the job?

The 'Blank Screen" feature is part of the Power control settings. You can set the time until the screen blanks quite low if you want.

Okay. What is the timeout for “Dim screen when inactive”?

I am not sure what you are asking. I do not use Gnome Desktop, so I have very different settings on my copy of Zorin. However, as I understand it, it is either going to be a slider or a drop down menu in which you choose the amount of time. The timeout will vary depending on the time you choose for the system to allow to pass before blanking the screen.
The “Dim screen when inactive” is similar. To save power, it dims, but does not turn off, the display. I THINK… that you can adjust the dim level, as well as the time. I do not know how far you can dim the screen.

Power Settings: