I don't know about the G-series models, but in my A590, there's a normal camera setting in the menu called Review. It lets me set how long the picture just taken will be displayed, and one option is "off". I use that setting for timelapse.
But that alone doesn't turn the display completely off. On my camera, I can turn off the display manually with the DISP button, then go into alt mode, then press the shutter to start the script, and the display stays off for the entire run. But, this doesn't work with manual focus, which I like to use to keep the camera from hunting. So the best I can do is plug a 1/8" jack into the A/V port, which seems to turn off the display, but really doesn't, and seems to save only a little power.
Maybe a G9 guy will have more useful advice.
