We are heading to Italy May 11 & the wife is freaking out about not having train tickets in advance. We will be going from Rome to Florence then Florence to Venice.
1. If you get tickets in advance are they good anytime or do you have to specify a departure time?
2. If we get tickets for a specific departure time and want to leave later is it a hassle to change your tickets?
Answers would help to calm my wife's anxiety.
Thank you
Mike

The way I understood it last time I was in Italy was that the tickets are good anytime but if you have seat assignments those are only good for the specific departure time. So you could still use your tickets on a later train but you run the risk of not having seats and standing the entire way. I would suggest buying the tickets a day or two in advance. No need to buy before you get to Italy. Just drop in to a local travel agency and buy them.

FOr these 2 destinations I suggest that you take the Eurostar trains because they are faster and more reliable than Intercity trains. It takes 1 1/2 hrs from Rome to Florence and about 2 1/2 hrs from Florence to Venice.
Eurostar trains require the seat reservation which is compulsory but included in the ticket price. Therefore you must specify the date and the time you want to take the train. There are trains every hour between Rome and Florence and more or less every 2 hours from Florence to Venice. The second class tends to be more crowded than the first of course, but the seats are comfy in the 2nd class as in the 1st class (less seats in the first class coaches though but they pass free newspapers).
The change rule is as follows: if you change the original ticket (date or train) BEFORE the departure of the original train you only pay 3 euros each as new reservation fee. If you change AFTER the departure of the original train, and within 24 hrs from the original departure time, then you will lose 50% of the fare and you will need to issue a new ticket.
Therefore I suggest that you reserve the tickets 1 or 2 days prior the departure, going either in a travel agency entitled to issue train tickets or directly at the stations.
No need to pinch the eurostar tickets at the yellow machines situated at the beginning of each platform.

Calmati, calmati...for those long hauls I would recommend you take the Eurostar 2nd class which is not that much more than the IC trains 1st or maybe less, but generally saves you on the longer hauls anywhere from 1/2 hr. to an hour. For Eurostar trains you will need to reserve a specific train and seat. At the high seasons and certainly from Florence to Venice, if you don't want to stand in the hallway of the IC train, buy your tickets in advance; these are popular routes. But not in the US.

First, visit http://www.trenitalia.it/ and punch your information in on the dates you want to travel. This is the website for Ferrovie dello Stato and it will show you times for all their trains. It will also give you the price when you click on a specific train and class.
No matter if you decide to go by open ticket or seat on IC trains or reserved on the Eurostar, when you arrive into Roma, stop by the station or by the American Express tourist office, and buy your tickets for Florence. When you get to Florence, while still in the station, buy the tickets to Venice. It saves visits, and you have the security of having the tickets (which will calm your wife) and the flexibility of checking the huge boards for schedules.

Changing tickets, Boulder is correct. You can apply open tickets to any train (as long as you have paid the surcharge if you travel the IC rather than the interminable diretti); you can exchange tickets that are not stamped for other ones, but this must be done at the window, and if you speak only English, this can take a while--so if you buy reserved seats, don't miss the train!

There are tons of automated ticket machines in these main stations, and while at least half seem to not work at any given time, it still leaves lots. But if you check your time in advance, you can buy them more efficiently. Also check the prices and the class of what you're buying by machine and compare them to the website.

Finally, don't forget to validate the ticket in the yellow box BEFORE you board the train. Every guidebook will remind you! At any rate, train travel is wonderful in Italy, and you'll enjoy the view.
Buon viaggio.

Another reason for calm--there are virtually hourly departures for the two popular routes you mention. This issue should be the least of your worries, especially with all the good advice you've received here.

I've used trains all over Italy and have never purchased tickets before the date I wanted to travel. Especially, on the higher traveled routes that you mention. It really doesn't make much sense because it "locks" you in (or penalizes you if you change your mind).

Get your tickets when you get there, maybe a day in advance if you're worried. Tell your wife all will be fine. Have fun.

Thank you everyone for your advice. We are looking forward to the trip and will buy our tickets at the stations.

Mike