I think this raises another point on realistic expectations. Florence is easily a ninety minute to two hour drive from the actual port, Livorno, if the traffic in Florence is actually moving. It would be realistic to expect your excursion from a ship to Florence to include at least four hours on a coach, often in heavy traffic. I saw one excursion that included Florence, Pisa and Lucca on a day trip - that is a long time on a coach and not much time in any of them.
I find cruises that refer to "ports" that include Rome, Granada/Seville, Paris etc. as being on a scale from amusing to disingenuous and would always advise a little further investigation as to where the boat will actually be berthing.
BTW Livorno is a great small city, with a number of excellent sites, beaches and restaurants and well worth a day's touring in its own right.