CDG to Montparnasse
 

We are arriving at CDG on a Saturday in September at 9:30am. Planning on taking the a Train from Montparnasse to Tours at either 1:56pm or 3:17pm. We are thinking of taking Les Bus Direct to the Montparnasse train station. The website says it take about 70 minutes. Is that accurate or will there be major traffic tie ups that we should take into consideration?

Any city can have traffic snarls and predictions are as reliable as gazing into a magic globe. But Saturday could enjoy less business traffic.The person with the most knowledge will be the taxi driver you hire from the official queue. Tell the driver you want the Montparnasse train station, not the Metro station. Even if you don't have train tickets in advance, you should be comfortable and maybe have time for lunch. Many, perhaps most, trains don't start loading until about 20 minutes before departure. If you have a reserved car and seat, just climb on board. If it is a general ticket, it must be stamped in a machine at the entrance to the platform.
This blog has helpful photos of Montparnasse and a diagram of the platforms:
www.Parisbytrain.com

Agree chance of traffic snarl is less on a Saturday, plus there is an express lane for buses. You should be fine on the bus.

BTW if there are more than 2 of you, it is just as economical to take taxi, as the fare is capped at € 55 to all locations on the left bank. Transit tiem should be no more and likely less than the bus.

Is there a specific reason why you wish to go into Paris first and not start your trip to Tours at CDG TGV?

There is a direct train to St Pierre-des-Corps (Tours' TGV station) leaving CDG TGV at 11:18am (Saturday, Sep 3 - you should of course check your actual travel date).
And even later connections which are not as quick or convenient as the direct TGV will at least save you the hassle (and money!) of having to get to Montparnasse.
The 12:48pm departures routes you via Angers (which is a bit of a detour and involves a 1:15hr stopover in Angers), but the total fare still is less than what you would pay for a taxi from CDG to Montparnasse.

I have taken that bus numerous times and plan to again in a few weeks. I really like it, and yes, that is an accurate estimate of time. It is actually better environmentally (not to mention for traffic) if every single person doesn't feel the need to take a personal taxi, I don't see the need to try to coerce people who are perfeclty happy with public transportation to take private cars.

I would agree with Cowboy1968 take the direct from CDG at 11:18 and in doing it that way, you make Christina happy environmentally too.