Venice to Florence by train - How long to wait after flight?

Wait til if and when you get to Venice so you don't lose your money on the business class seat if the flight is delayed or canceled.

The bigger question is, Why fly to Venice to go to Florence? That doesn't make a lot of sense. Going directly or even into Milan would make more sense. There is no "business class" on trains - either first or second class. There is no customs or immigration if coming from Nice. But then you need to get to the train station. If you are going to do that and you have time at this point, I would book a Super Economy, 2nd class ticket for about three to four hours departure after your arrive. It will be super cheap and possible a throw away ticket if don't make that train. Then you would have to buy a full fare ticket but no worse off than if you bought the ticket on arrival.

A SE, 2nd class fare in Oct is 20 Euro. That same walk up fare on arrival would be about 60 euro and a first class ticket could be as high as 125 euro. So your are risking 40 euro if you don't make that reservation.

From Nice, there are no customs, basically a domestic flight. Business/1st tickets are 67 EUR Base Fare per person, Advance purchase Super Venezia tickets are half price, but if you miss your train, they are wasted and you would have to buy new Base Fare tickets. Fast trains are at least every hour and you don't save all that much by rising advance tickets. Besides, your desire for 1st class indicates that money is not that big a deal for you.

You can take the Aerobus to Venezia Mestre station, or a land taxi as you prefer.

We will already be in Nice. There isn’t a flight from Nice to Florence , so we decided to fly to Venice. We will return to Venice a few days later by train, then eventually fly back to the US through London. It’s not that money is no object, it’s just that time is more precious!!

Look at a map. I cannot believe you cannot get between Nice and Florence via air -- maybe not a direct flight but you get there via air easier than what you have suggested. Consider flying to Pisa.

Sounds like you already have your plane tickets. In this situation, I would just wait and buy the train tickets at Venezia Mestre train station. 1st/Business class tickets (and, yes, Frecciarossa trains have a Business Class...) almost never sell out, so no worry there. The downside to waiting is of course you pay more. Even though this is a short flight, and from a Schengen country, there is absolutely no way to predict if/how long a flight delay will occur, which is why I would wait.

Once landed, you'll be off the plane, collect any checked baggage (can be quick, or could not be quick) and be out the doors of the airport. You'll then need to take a short (approx. 20 min.) bus ride to Mestre station.

That sounds like a great plan! Thank you all for the suggestions!