I believe they wont let you enter into the terminal area till 10am the vast majoirty of the time, though I have read where people get in a little earlier from time to time. In the past, we arrived a slight bit earlier, say 9:40ish and they had the early arrival cars line up till they opened then we headed on in to drop off luggage etc.
We were also considering booking the brunch when I saw it open online, but dragged my feet and missed out.