I'm trying to determine if we could make a 12:05p train out of Montparnasse after arriving in Orly at 10:25a. We are two couples coming from Rome, going to MSM on a Saturday, and then returning to Paris the next day. The next train leaves at 14:05, arriving St. Malo at 17:35. So, I'd much prefer to try to catch the earlier train as that would give us a little more time at MSM, although we plan to view it the next morning to avoid the crowds. Thanks

It would be doable, but tight. It depends on how long it takes you to actually get out of the airport after landing. It takes around an hour on public transport to get from Orly Ouest or Sud to Montparnasse.

The Air France bus between Gare Montparnasse and Orly was quite quick when I took it (more like 20 minutes, I think).

You might, or might not....

As mentioned, it will depend on how quickly you get out of the airport...and at CDG that's anyone's guess.

The Air France bus...if you catch it right away, may get you to Montparnasse in 40 minutes or so, you need to allow at least an hour...

And then you'll need to allow a half-hour or so to get your tickets at the station...

I sure wouldn't buy nonrefundable tickets ahead of time for this trip...