Leave after breakfast, arrive for lunch
At 4,430 miles London to Miami is a genuine long-haul flight, and the choice of cabin decides whether it is one leg or two. A Gulfstream G650 or Global 6000 flies it non-stop in about nine hours; a Falcon 900 or Legacy 650 stops for fuel, usually in the Azores or Bermuda, and lands about an hour and a half later.
The five-hour time difference works in your favour westbound. A late-morning departure from London lands in Miami mid-afternoon local time, in time for dinner on the water. Opa-locka's private terminal clears customs in minutes and puts you in Brickell or South Beach twenty minutes later.
Miami is a base for a great many large-cabin aircraft, so the return leg prices well, and a round trip with the aircraft waiting a few days in Florida is often the better value than two one-ways.