Ronto Roasters is open at park opening time, serving a breakfast menu (the Ronto Morning Wrap is delicious). The Milk Stand opens early too. Docking Bay 7 doesn't serve breakfast items (nor does Kat Saka's Kettle), so it doesn't open until "Lunch" at 10:30 or 11am. The shops are open right at park opening as well.
My family had a great time just hanging out in Galaxy's Edge on a Saturday morning -- it was relatively uncrowded between 8:30 and 10am (if you were in the outpost area not too close to Rise).