Pisa trip

You don't need to take a whole day to visit Pisa. It's about an hour by train from Florence so about 2-1/2 hrs travel time, 2 hrs if you only want to see the tower, cathedral, baptistry; more if you want to have a meal and maybe visit a museum. Leave Florence early and be back by about 2:00 or 3:00 in the afternoon. If you want to climb the tower you'd have to get tickets ahead for a specific time to avoid wasting a lot of time in line. I found it fascinating as a 3 hr stopover between two other cities (did not go up the tower), but I could take it or leave it. It's only worth it if it's really important to you.

Most people will find two full days in Florence adequate.

You have more than 3, so you do have time for a day trip.

However Pisa doesn't offer much more than a photo opp with you trying to hold the leaning tower up straight.

I'd choose Siena for a day trip. Or maybe Lucca, if you want to go toward Pisa. Then once you are done with Lucca, take a short train ride to Pisa before heading back to Florence. One hour or two in Pisa is enough, and trains back to Florence from Pisa are plentiful (60 a day in each direction) until well past 10pm.

We are going to Lucca & Pisa in one day from FLR by train. We were told this makes a good 1 day trip

In my humble opinion, two days in Florence is not enough to get to know the charms of the city - there are just too many sights. Plus, a lot depends on what two days of the week you are talking about. Look closely at the business hours of the venues you are planning to visit. If your 3 days includes a Monday, you may want to use that day for a day trip.

I personally found Pisa very underwhelming. I, however, loved Lucca. You can do Pisa in the morning and then escape the coach-tour hordes by going to Lucca for the afternoon. I would definitely plan on being Duomo as early as you possibly can. I found the tourist crowd there to be the worst of my two week Italy trip.

It's all very easy by train but some people choose to travel Pisa to Lucca by bus. One word of caution about the Pisa San Rossore train station (closest to the Duomo and tower), it is unattended so either know how to buy tickets out of a kiosk (and test your credit card beforehand) or pre-purchase your tickets in Florence.

We got off our train (from Monterosso) at the Pisa San Rossore station and walked 5 minutes to the Field of Miracles. We spent 15 minutes looking and taking pictures, jumped on a bus then the "Pisa Mover" to the airport to pick up a rental car. That was enough.

In my humble opinion, Pisa is very likely the most over-rated hot-spot in Italy. There's the famous leaning tower with cathedral and baptistry surrounded by a massive lawn (the white marble against the green grass makes for some impressive pictures I'll admit) however, THAT'S IT. No offense to any locals but, there just wasn't much to the rest of the town and the absurdity of the world's tourists taking idiotic pictures just made the whole scene surreal.

Lucca on the other hand, well worth it, possibly one of the most underrated locations; hard to compete considering Florence, Cinque Terra and Pisa are all nearby. In fact, I've come across more people who after visiting and staying in Florence for the first time around, after visiting Lucca all agreed that their second trip, they'll be staying in Lucca instead and visit Florence as the day-trip destination.

Siena should be at the top of anyone's list of day-trips from Florence. Trains or, buses, plenty of transportation options to visit Florence's long-time rival.

Zcorsair, You've got to go back. You missed the 12th century duomo that changed architecture forever, the Pisano pulpit was the segue to Renaissance sculpture, the fabulous National Museum of San Matteo, the world's oldest botanical garden, the world's oldest Jewish cemetary, and a whole lot more.