Hey Roban,
I know what you're talking about...The light sensor is on the center dash next to the windshield..it's the little bubble looking thing...Mine takes a few seconds to adjust the screen brightness after I back out of the garage..but it does it..I have found in the past that if a film of dust or anything is on that sensor, it will take forever to adjust to the brighter outside ambient light..Cloudy days and late afternoon light will also make it sluggish to react..
Just make sure it's clean...There is no adjustment to the setting on this that I know of.
BTW..do you mind mentioning the year and style of your Terrain ?