Rome FCO to Venice train - buy early or no?

AD,

Your comment about being "wary of buying tickets in advance im case our flight is delayed" is the main reason why many of us on the forum don't recommend buying tickets in advance. While you can save money (especially for a group of six), if you miss the train you've booked, your tickets will be worthless and you'll have to buy more at Base fare (full price).

Depending on circumstances at the time, it could be 08:30 or so before you deplane, get through Passport control, collect your luggage and get to the airport rail station. There's really no way to predict what conditions will be like on the day your flight arrives.

The safest approach would be to simply buy tickets when you arrive at the station for the next train heading to Venice. If you're wiling to take some risk, the other approach would be to buy a discounted ticket for the direct 11:08 train. Find a coffee shop or have a light lunch while you're waiting.

If you'd rather leave the airport as soon as possible, there's a departure at 08:57 that you might be able to connect with. That train involves taking the FL-1 from the airport to Roma Tiburtina and then connecting with the Freccia train there. One very important point to note is that if you buy the tickets for that route locally, you MUST validate your ticket for the FL-1 prior to boarding the train, or you'll be subject to hefty fines which will be collected on the spot.

As Ken said, there is no way to know what conditions will be the day you arrive.

Assuming something in the " average " range, I do not see that a long wait is a real concern .

By the time everyone hits the restrooms, gets some sort of snack, I believe you will find you have little "thumb twiddling" time

When ticket discounts were more substantial (i.e. 19.90 euro to Florence), I used to book the direct 11:08 train. I felt under 20 euro was worth the gamble. My flight usually arrived on schedule around 9:15, and I can tell you from experience it was a long boring wait for the 11:08 train to depart. Even allowing for time to walk over to Terminal 1 to buy items for lunch (imo the sandwiches sold there are better than those sold at Terminal 3), there was still a lot of waiting around time. You're talking another 1:45 of waiting. If you want to save up to 50% on tickets, not have to change trains at Termini and don't mind the long wait, then pre-purchasing tickets for the 11:08 train could be a good option. If you prefer to be well on your way to Venice by the time the 11:08 train departs, then it's probably better to bite the bullet and buy Base fare tickets upon arrival.

Since the FL1 airport train is € 6 cheaper than the Leonardo Express that goes to Termini, if you departed to Venice from Roma Tiburtina you would save € 36 .

Did you check out Italotreno's discounted and walk-up fares from Roma Tiburtina to Venezia S. Lucia? Italo runs less trains, but they often have better prices and more flexible T&Cs. They don't have a counter at FCO, but there is free w-fi in Fiumicino. You can buy all train tickets online up to 15 minutes before the departure time.

Odds of all trains from both companies being sold out are very small. If trains on a route routinely sold out, railway companies would just add more cars and make more money.