About how long does it take to get through customs at the airport in Rome? I am asking because we are thinking about taking a train from the airport that departs at 11am. Since we arrive at 9am that would give us two hours.
It's impossible to predict. It depends on how many flights arrive simultaneously. Customs is not an issue, it's a walk through the green line (nothing to declare) and I've never been picked for random check in over 40 times flying to Italy. But lines may form at Passport Control (immigration) if you are coming from outside the EU.
Also in my experience FCO is horrible when it comes to baggage claim. Sometimes the wait is unbelievably long before bags appear.
The other big issue is the flight arrival/landing. There is no real guarantee that your airplane will land on time. That is another unknown.
So moral of the story, it is not a good idea to purchase the train ticket ahead of time within a few hours from landing. I understand the savings may be appealing, but discounted tickets are non refundable/changeable. If you miss that train, you have to buy a brand new ticket anyway. I would buy the ticket at the airport station when you arrive. If you miss that train (I presume you are taking the 11:08 to Florence/Bologna/Venice) there are plenty more departing from Roma Termini. You just have to take the Leonardo Express to Termini from the airport (32 min).
We've had flights arrive two or more hours late. In addition, there isn't anyway to know how long immigration will take at any given airport at any given time. With those thoughts in mind, consider just buying the train tickets upon arrival. It will probably cost a little more, but at least you'll get on the train.
And if your flight arrives early and passport control lines are minimal, you may be able to catch an earlier train than trying to have enough of a time cushion.
This year we had two late flights to Rome. One by an hour the other due to late arrival in London 4 hours late. Prior to this we've been on time but there are no guaranteed and I wouldn't prebook.
Also in my experience FCO is horrible when it comes to baggage claim.
Sometimes the wait is unbelievably long before bags appear.
Had that same experience at FCO once so I wouldn't count on making that train.