What time can we take a train?

What??? You are flying into Rome, going to hotel in Rome, then are going to Florence that day by train? Is this a day trip to Florence by train or are you paying for a hotel in Rome and Florence or are you just storing bags at Rome hotel before going to Florence?

I wouldn't book anything earlier than 3:30 or 4 - so many variables - long waits at passport control, traffic, flight arrives late. The other problem is if you book now and your flight is late and you miss your train you may well be out the full fare you paid and have to buy tickets again.

Need a clearer understanding of what you are doing. Don't understand hotel in Rome. Arrive Rome 11.40 from where? International or domestic? Huge difference. Termini is not convenient to Navona but Tiburtina is even further away. Very, very rough guess would be 4 or 5 pm. Would not purchase ticket until you are in Termini. Too many uncontrollable variables.

I also would not buy train tickets in advance for a day you arrive by air. They cost about $55 one way, per person in standard class if you pay full fare on the day of travel. Advance purchase discounts are normally not refundable or changeable, especially after the departure of the scheduled train. From either Rome station, Trenitalia has more fast-train departures to choose from - roughly two per hour to Firenze SMN on "le Frecce" trains- than does Italo.

ts,

I'm also somewhat unclear on your plans. Are you arriving in Rome, staying a few days and then going to Florence? You'll probably find that you can take a train at whatever time is convenient, as there are numerous trains on that route every day.