40-50 miles is a good 'dawn to dusk' day sail and if inexperienced you do not need to be sailing at night in difficult waters like the Keys or making night entries into places like Snake Creek. (somehere on here there is a description of what happened to an inexperienced sailor entering Snake Creek at night)
Theoretical speeds, 6 knots for smaller boats, are rarely achieved in practice and a few squalls and stormy days will disrupt the schedule even more.
While the trip is only about 300 miles and in delivery
mode would take 3 days or less I would plan at least 10-12 days for a leisurely, no stress, trip and make sure I arrived at each anchorage or marina at least 1-2 hours before dark.