I never thought to look for Miami, but my guess is that you could possibly see it from the Magic on its western itinerary. I'm thinking that for the eastern, or from the Wonder en route to Nassau, the ship would be too far away to see. A straight line between Port Canaveral and Nassau would be about 80 miles or so out to sea at its closest point to Miami. The Magic follows roughly the same path on the eastern, heading further east to cut between Abaco and Eleuthera Islands.
I'm not sure how close to the coast the ship would be for the trip to Key West on the western. If it had a casino, I'm guessing it would have to be at least 12 miles out to sea in order to open it (the casino), but since there isn't one on the Magic, it's possible the ship is closer to land.
I would guess that it would be roughly between 1:00 and 2:00am when Miami would be visible, probably closer to 2:00. I think Miami is about 200 miles from Port Canaveral, give or take, and the ship usually makes about 20-25 knots on the open sea.