We land at FCO at 2:35pm from the US on a Wednesday in June. We are immediately heading to Florence. I'd like to buy train tickets to Florence ahead of time so as not to risk paying 2-3x for last minute fare. I'm willing to risk losing that ticket (around 25 euro per person) if we don't make the train. Considering that the incoming plane could be a little late, passport control/customs, getting lugguage and getting to Termini, what is the earliest time I should safely book a train from Termini to Florence? I'm thinking somewhere around 6pm. Yes, I know Tiburtina is an option and I'l figure if we go to Tiburtina, it'd need to be about an extra 15 minutes.
6 pm sounds about right
I think 6:00pm/18:00 is a reasonable time to book ahead of time and you could assume you'll be there by then. Even if your plane is late and immigration is backed up (there have a lot of posts about long wait times at FCO) and with the train trip to Roma Termini this seems like generous cushion.
Most likely scenario is everything goes to plan and you're there an hour or an hour and a half early so you get a coffee and a sandwich, maybe use the ATM as you wait for your train. If that scenario is worth saving the extra money to you then I think you've got a plan. It sounds better to me than booking at 5:00pm and sweating it the whole time.
You're on vacation so relax a little because Florence isn't going anywhere.
=Tod