The RER is great if (a) you have little luggage and (b) it's not on strike. Just keep track of your belongings and be careful not to doze off on the ride in and you'll be fine. Figure about an hour to arrive in the 7th.
I usually ride from CDG to close the other end of the line (Courcelles sur Yvette) after 10:30 PM, with a forced change that I choose to do at Luxembourg. Never had a problem. It usually is longer than the flight, though

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