Megan, first, just for the record, Florence is the principal city in Tuscany, so Florence and Tuscany are not different places. If possible, I think the best thing would be to dedicate that last day waking up in Sorrento to travel, and arrive at wherever you are headed in Tuscany by dinner time. Best bet I think would be to travel much earlier in the day, by train, from Sorrento to Naples to Florence, and then rent your car, and drive to your ultimate destination, assuring you will arrive while it is still light out. If you want to save some time and hassle, especially if you have much baggage, arrange for a taxi or car service to pick you up at your hotel door and deliver you to the Naples train station. That should take about an hour and cost about €100, not too bad for 2 people with bags, even better if you are more than 2 people. If you need to travel later in the day, check train schedules and still follow this plan, but spend the night in Florence and rent the car the next morning. By the way, what season are you traveling, and just where in Tuscany will you be staying?