Changing trains at Roma Tiburtina station

We land Saturday 23 March at FCO 12:35

Train reservations;
14:12 FCO to Roma Tiburtina arr @ 15:00

15:10 Reg Veloce #2314 Roma Tiburtina to Chiusi-Chianciano Terme @16:55

17:14 Reg #23474 Chiusi-Chianciano Terme to Asciano-Monte Oliveto Maggiore @18:14 (our destination) for stay at Roberto's bnb

someone knows the usual platforrms these train use this could change last minute.

Trenitalia's mother company knows better: http://goo.gl/e5cwCw

The intended departure track of RV2314 is #6, but you'd better check on one of the "Partenze/Departures" monitors hanging around. Track is Binario or Bin. in Italian.

Tiburtina's building may be quite big, but the tracks area is quite compact. Take an escalator going up, walk to your track, take an escalator going down.

If you will have a working phone, download the Trenitalia app. Enter the train numbers in the “Train Status” section and it will give track numbers of your arriving train and departing train. You should be able to make the connection. However, I also think that taking the Leonardo Express from FCO to Termini would give you more time to get train 2314. The trip to Termini is faster and the train originates at that station and departs at 15:02.

Okay, what everyone says makes sense. I purchased the train tickets through the Trenitalia website and mistook Roma Tiburtina as the main station. Is it possible to cancel the reservation and start over using the Leonardo Express from FCO?

Sally, I listed out all the stops for your train (15:10 Reg Veloce #2314 Roma Tiburtina to Chiusi-Chianciano Terme @16:55). The list is below.
As you see, it starts from Roma Termina at 15:02 (6 minutes earlier). Your ticket is almost certainly valid from either Rome station. If you want to, just get on at Roma Termina.
As this is an "R" train (regionalle), there are no reservations and your ticket should (AFAIK)be valid on the next train at 16:07, should you miss the first one.

R 2314 Route from the 23.03.19
Roma Termini dep 15:02
Roma Tiburtina arr 15:08 dep 15:10
Orte arr 15:42 dep 15:52
Attigliano-Bomarzo arr 16:02 dep 16:03
Alviano arr 16:10 dep 16:11
Orvieto arr 16:25 dep 16:26
Allerona-Castel Viscardo arr 16:34 dep 16:35
Fabro-Ficulle arr 16:43 dep 16:44
Chiusi-Chianciano Terme arr 16:55 dep 16:58
Castiglione del Lago arr 17:08 dep 17:09
Terontola-Cortona arr 17:18 dep 17:19
Camucia-Cortona arr 17:23 dep 17:24
Castiglion Fiorentin arr 17:30 dep 17:31
Arezzo arr 17:43 dep 17:44
Montevarchi-Terranu. arr 18:06 dep 18:07
S.Giovanni Valdarno arr 18:11 dep 18:12
Figline Valdarno arr 18:17 dep 18:18
Firenze Campo di Marte arr 18:38 dep 18:39
Firenze S.M.N. arr 18:48

If you purchased Regionale tickets on-line, they will be valid on any regional trains on that route for up to 4 hours. There are also departures from Tiburtina that get you to Asciano at 16:02, and 17:22. The 16:02 will require another change at Orte. So even if your plane is late, you can still get where you want to go on later trains without changing your ticket.

All of you are wonderful to respond to my question. Thank you for encouraging me not to start over.

I am curious about these trains that would get me to Asciano earlier. I need to spend my time—figuring out how to get to Asciano earlier. I am also going to attempt to catch the Lernardo Express to Roma Termini. Thank you.

The tracks where the regional trains arrive and depart at Tiburtina should be close together. If you were changing to a high-speed train (which you're not), then the walk between tracks would be longer.

As mentioned above, if you should miss your connection at Tiburtina just take the next regional train (not Intercity) heading to Chiusi. You might want to research times for later trains and make a note of them in case they're needed. I did a quick check and found one about an hour later (one additional change in Orte), and it would be covered by the ticket you already purchased.

If you purchased Regionale tickets on-line, they are not valid on earlier trains, only trains beginning with the one shown on the ticket and following trains for the next 4 hours. No use worrying too much now, you don't even know for sure if you current flight from Frankfurt will arrive on time.

PS, If you do arrive at the station early, you can buy tickets to Tiburtina on earlier trains at 8 EUR per person. There are trains at 13:27 and 13:57.