Typically the fast food places open early--and Starbucks may even open early.
And usually the drive through lines are a mile long once they open as the people who hit their first stops are getting hungry.
Chick Fil A was the only restaurant open in the food court in a mall I went to once--and that line was a mile long. As was , Panera that was located in another mall. Those not serving breakfast were not open.
My advice--we usually pack sodas (diet coke) and bring survival snacks and then just eat when we get home. Whatever is open usually gets swamped and quickly. I have done BF in Marietta/Roswell, GA; Tampa, FL, and Melbourne, FL and that is what we have noticed.
If you want real breakfast, your IHOP, Village Inn, Steak N Shake, Perkins type places may be considerations if they are open 24 hours.