Screen timeout with Guided Access

Hi I am using an iPAD with Guided Access turn on in our lobby for visitor management. Guided Access is turned on so that visitors or staff cannot exit the app or switch to anything else. However, at the end of the day around 5PM or so, I would like the ipad screen to go black/go into power save mode. When staff return in the morning they can wake the ipad and visitors can check in.

I was monitoring it in the app with Guided Access on for a few minutes and the screen stayed on.

How can I set it to go black after 8 or 9 hours?