Enough time at CDG? Flight to Rennes

That's a 5 hour, 25 minute cushion. Barring something bizarre, that should be plenty of time for your layover.

Just take a train. It's not that far up to the coast.

Yes, you can get a TGV direct to Rennes from the train station at CDG. No need to fly.

I've done this transfer and you have plenty of time. Just be aware that you'll be changing to terminal 2G, and you can't walk there. There's a bus that keeps you airside once you go through passport control.

Thanks for the information everyone! Have scrapped flight option for train.

T - How much time does the transfer by bus take to get the train departure spot at CDG?
Looking at the train schedules: there are three options we could take from CDG to Rennes.
The first leaves at 8:49 - which is cutting it VERY close. The next at 9:19 is 4x as much and the third option leaves at 12:48 which will be fine, just require a wait at CDG.
If I book the 8:49 and we miss it - can that ticket be used towards the purchase of the 12:48 train?

Do you know what terminal you are arriving into at CDG? It is not very likely that you will have to take a bus to the TGV train station, which is connected to one of the airport terminals.

No, unless you buy a more expensive, fully refundable ticket, and are able to cancel it before the 8:19 train takes off, (a key element), you wouldn’t be able apply any purchase price towards a later ticket. Tickets for the TGV are only good for the specific train for which they are bought.

It’s probably why the 9-something tickets are more expensive (I am speculating here that more people feel comfortable that they will make the later train).

No, unless you buy a more expensive, fully refundable ticket, and are
able to cancel it before the 8:19 train takes off, (a key element),
you wouldn’t be able apply any purchase price towards a later ticket.
Tickets for the TGV are only good for the specific train for which
they are bought.

Kim is actually in Paris so I would defer to her if I'm mistaken, but it's my understanding that starting from 9 May the SNCF has simplified its fare structures so that all 2nd class tickets (aside from Ouigo tickets) now have the same fare conditions:

• Up to 30 days before departure, free exchange/refund (plus any difference in fare)
• Starting from 30 days before departure, €5 exchange/refund fee plus fare difference
• Starting from 15 days before departure, €15 exchange/refund fee plus fare difference
• Starting from 30 minutes before departure, ticket can be exchanged only twice for a trip on the same itinerary on the same day, not refundable after exchange
• After departure, no refund, no exchange

I did a quick dummy booking of CDG-Rennes TGV tickets on oui.sncf for tomorrow (15 June) as well far out into the fall (12 Sept) and both the €90 fare for tomorrow's 8:49 departure as well as the €30 fare for the 8:49 on 12 Sept have the same fare conditions as below:

Billet échangeable et remboursable avec retenue de 5 € à compter de 30 jours avant le départ, portée à 15€ l'avant-veille jusqu'au jour du départ. À partir de 30 minutes avant départ du train, billet échangeable 2 fois maximum uniquement pour le même jour et le même trajet et non remboursable après échange. A la retenue s'ajoute l'éventuelle différence de prix entre l'ancien et le nouveau billet. Billet non échangeable et non remboursable après le départ.

Thank you Kim and Andrew!

Appreciate the insight. I hope this next question does not sound silly - but any thoughts on how necessary it is to purchase the CVG ticket to Rennes in advance? Likely to sell out (or just solely dependent on the day)?
Would your advice be to just purchase the 12:30 fare where unless our flight is just cancelled we will for sure be able to make the train departure?
I am thinking maybe purchase the 12:30 as a safety net and if things gloriously work out and we can make the 8:48 train- we will just buy those tickets and eat the cost of the others!

Or exchange them for the earlier train if outside the 30-minute limit and the line is short. You’ll need to pay the fare difference.