That is a firmware or system backlight setting. Basically, its it for everything outside iFly GPS or iFly Streets.
We actual do some overriding of that inside our navigations software. Currently, this Day Night Mode time setting will not work for your intended use. We are working on an Auto Day/Night Mode. It's making its way up the Wish-List.
Sorry for any confusion or frustrations. Hang in there, we'll get it added.