Travel Time from CDG to TGV

There's no deadline to buy train tickets, but since TGV is a reserved train, it can sell out, or one class of service could sell out. I don't know how often that happens, but arriving early in the day means you have more possible departures that could work to get you to Avignon on the same day.

If there's any delay in your plan, then your 2.5-hour cushion might not be enough. Advance-discount tickets can't be used on anther train and you'd have to buy a new ticket at full fare (again assuming spots are available).

In one personal instance, I have had my flight from Seattle to Paris both depart and arrive an hour late. Another year, I missed my flight connection at CDG (maybe I had an hour or a bit more?) due to 45-minute lines at passport control. But that airline had to put me on the next flight, whereas the TGV does not. (Unless maybe TGV tickets are booked through some airlines; I don't know the details.)

Where are you flying from? And how reliable is your airline for punctuality? You really have to weigh up pros and cons - possibly waste a ticket by missing the train due to flight delay or pay more on the day for a walk up ticket.
2.5 hrs would be a 'best case' scenario. I would look at possibly 2 hours to get thru CDG, an hour to get across Paris to Garre de Lyon, and add 2 hours to have 'up my sleeve' - so 5 hours after you land.
TGV 6113 departs at 12.37pm.

Thank you for the replies! I should also have mentioned that we are taking the train from CDG. We do not need to travel to Garre de Lyon. I am struggling with taking my chances on the 2.5 hours or waiting around and scheduling the 4.5 hours later. Thank you for the advice.

I don't want to spend our first day in France sitting in a train station for a later train departure to Provence.

Don't spend your day in a train station. Spend it in Paris.

When you buy a plane ticket with a connection the carrier is obligated to get you to your destination even if their delay causes you to miss the 2nd flight. When you're changing to a different mode like plane to train, nobody is responsible for making it work. The past few flights to Europe we've been on have been delayed in arrival from 30 minutes to 3 hours. As the earlier post by Laura shows, this is not unprecedented. You can look up stats for your flight at http://www.flightstats.com/go/FlightRating/flightRatingByRoute.do But stats don't matter, in the end it only matters what happens to your flight.

Often, of course, flights arrive on time. But to make your plans based on it is to risk your TGV ticket price (and even for refundable/changeable tix you typically need to do so before the train leaves the station, not always easy if you're on a plane over the Atlantic) and the cheapest TGV tickets are good for the listed trip only. And if you miss your train then you'll need to buy full-fare walkup tickets to replace them.

One alternative is to cool your heels for a few hours and book a later train you're more likely to make. Our preference, maybe not for everyone, is to spend the nite in our arrival city. If your flight to Paris is due in at 7:30am it may not make that exact time, but odds are pretty high it makes it in that day! So if your plans are just a ride into Paris on the RER then the hassle of meeting a deadline is gone. Walk around Paris, visit a museum, drink coffee, have a nice dinner. Leave early the next day for Avignon and you can be pretty sure this plan will work out no matter how delayed your plane, how long the line for customs, etc (unless the French trains are on strike, but that's another post...)

It costs more this way, an extra nite, but to me its like an insurance policy on the trip getting off to a smooth start.

I'm with Bill. There are just so many ways you can be delayed: mechanical, weather, baggage (unless you only have cabin baggage), long lines. I once missed a 7.30 p.m. play in London because of a mechanical problem with a plane (and that was a 5-hour flight due to land around noon!). If the plane is late flying into your departure airport, you could be delayed.

Look at the full price for TGV tickets. That's what you'll be out-of-pocket if you miss the train. There are worse things than spending a day in Paris.