We're looking at an 8:40 AM Saturday European arrival at Orly, and a 12:05 PM transatlantic departure at CDG.

Should we be concerned about having enough time for this connection on Saturday morning?

I would be concerned because the general recommendation is to be at CDG 3 hours ahead of time for an international flight. Taxi or RER are the only option. The taxi would be faster if there are no major traffic jams.

And as it takes a good hour at best airport to airport by RER - so it's not feasible if you must check-in 3 hours early

3+25 is a very tight connection and you have no guarantees that your ORY arrival will be on time.

Usually I recommend the AF Bus from ORY to CDG but you will not have time to wait for the next bus departure. Immediately board a taxi when you arrive at ORY.

Remember that the TSA is now involved in approving passenger lists on flights to the USA so late check ins may no longer be accepted if you reach CDG any later than planned. Check with your airline but I seem to recall the check in cutoff time by which the check in process must be completed as being approximately 90 minutes before departure.

I should encourage you to change your flight if at all possible.

I appreciate all of the advice, and have taken it to heart.

I think I can change the 12:05 PM departure to 1:10 PM. That should help.

The Air France bus also connects CDG and Orly. I think it considers the maximum transit time to be 90 minutes between the two airports (usually less...).

Meanwhile, the RER B takes less than 90 minutes between the 2 airports, with almost no delays ever.

Putting in a departure time of 10:00 for good measure, I was given the following time by the RATP site for using the RER B:

Départ à 10h02
Arrivée à : 11h25
Temps de parcours : 01h23

I would allow at about 3 hours from scheduled arrival at Orly to get to CDG. We always allow at least 3 hours for a flight departing CDG. Though, we've almost always had 1-2 hours to spare once through security, if things are backed up at check-in or security, all bets are off.

What will you do if you miss your flight at CDG?

What will you do if you miss your flight at CDG?>

which even with a 1:10pm departure still means you have about a 50-50% chance if everything goes right

and at paris airports do NOT expect anything to go right when you need it - long lines at baggage carousels - Customs, security, etc.