What boat? Do you know your range? Cruise speed. Burn rate at cruise?
The trip is a piece of cake, just plot your course. Head south until you clear Cape Romano, then SSE to Cape Sable and East Cape and to the Yacht Channel as you approach Marathon. Naples on the Gulf to Marathon is 105 miles, give or take a few.
If you're running the trip in one day, from the inside of Channel 5 Bridge (which is one of the alternatives to get to Hawks Channel) to ocean reef is about 60 miles. So, if the weather gods are with you, the trip is entirely doable in a day.
If you want to stay on the inside, you can actually run up through Card Sound and out Angelfish Creek. This route would take you a little north of Ocean reef so you'd have to double back a few miles once you got outside.
Or you could cut through Adams Cut, or Tavernier Creek (fixed 15' bridge), or Snake Creek.