We just disembarked the Dream in Miami last Friday, the 16th. Our flight was at 10am. We skipped the sit down breakfast and ate at Cabanas at 7. Our children are grown so it's pretty quick for us. Express Walk off was delayed until around 7:50. We still got to the airport by around 8:30am (Uber) and got our bags checked and at the gate by 9am. We have TSA Precheck so that helps speed our time getting through security.
We did the same thing last December and I'd do it again. The next non-stop flights for us were 2pm I just can't see sitting around the airport for several more hours unless it was a massive $ savings. I think 10am, give or take 5 minutes, is the earliest flight I'd choose from Miami.