I fly in and out of Terminal 1, so this would just be a guess for terminal 2. If you have luggage to pick up from your flight, and your flight lands at 18.05, I would suggest a TGV departure of no earlier than 18.45 (time to walk to your baggage claim area, go through passport control, pick up your luggage, and walk to the TGV station at terminal 2).
I'm getting the TGV from CDG to DLRP for the first time next month, my flight lands at Terminal 1 at 18.30pm, and I'm intending booking a TGV for around 19.10 (but I have no luggage to pick up).
For a return flight from CDG at 17.05, you want to be at the airport for 15.05 ideally. So a TGV leaving DLRP at around 14.50 or before would be fine for you.
I always book the cheapest TGV ticket for our return journey, there are explanations of the differences in the flexible tickets etc on the RailEurope site, when you click on a ticket price

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Hope this helps,