That means 24 hours to reach the continental shelf location in uestion from about say Key West.

Do the math. That leaves out about half of the Gulf.

Gulf is about 950x600 miles. MS can make 700 miles in 24 hrs. Once at the entrance (midway from key west and Cancun) what is left would be the entire gulf. Looking on google earth, it could be that the drop off of the shelf could be the rim.