CDG to Senlis or Chantilly for a few hours

Have you checked how early you need to check in for the second flight? Is it to Canada, Europe or to the USA? One reason I ask is that airlines have tremendous pressure to deliver check-in passenger data to U.S. security computers within a tight time frame-that's aside from the danger of a long line for Economy check-in, or traffic jams outside CDG.

Although I would also like to visit Chantilly, the excursion sounds unwise. And because I would not even do it without a round-trip limo rental in advance, it would be very expensive. Do you dare to wait for a cruising cab that's willing to go to CDG from Chantilly? Or take the word of a guy in the CDG line that he'll come back for you? I can't recommend a company because I've never used other than a Paris cab (or the RER) to get to CDG.

Although I usually subscribe to the idea that it's no longer necessary to speak some French to visit Paris, because of your dependency on an independent driver, I would suggest that decent French would make this excursion a little safer. Unless you have an unlimited "executive travel" budget.

Where is your second flight to? (I presume your 6 am arrival is from the States?)

First of all you have to calculate IF your flight arrives on time, 1hour if all goes well to clear immigration and pick up your bags and walk through customs. Sometimes 1.5 hours. anyway, if you arrive on time, it's 7 a.m.

For a 2 pm departure, you need to be at the airport at noon.

So your real window is 7 am to noon, from my perspective. You have NO time to be taking trains and making changes, and the Chateau in Chantilly is a bit of a hike from the train station (not too far for anyone who wants to do it or who's taking the better part of a day to go there , but too far for you to be dealing with.)

So you need a taxi to Chantilly - say it takes you 45 minutes to get there. It's now 8 am or 8:30. Guess what - the chateau doesn't open until 10 am (or 10:30 in low season, but I presume you're coming in the summer). So you go have breakfast somewhere, wander around.

Then you go into the Chateau and around the grounds from 10:00 to 11:15 or so, when you need to get your taxi to go back to CDG to make it there by noon for your check-in for your onward flight.

So basically you have to decide if it is worth it to you to go through all that for little more than an hour on the grounds and in the chateau. Only you can decide!!

You might take the train into Paris and have coffee and a stroll near Notre Dame and pick up a picnic lunch to take back and then get on the train by 11 to be back at 12 for a domestic flight. If your ongoing flight is to the US or Asia, you need to be back by 10. It is far too risky to try to get to a place without reliable transportation to the airport. And Senlis in particular involves train from Paris and bus connection -- and in our experience the bus to return did not come and we ended up taking one 45 minutes later than planned.

In addition to the time estimates you've gotten for getting out of the airport and the time you will need to be back at the airport in order not to miss your next flight, there's the time it will take to leave and retrieve your bags at Baggages du Monde. If there's a line for either the deposit or the withdrawal, you will lose further time.

Unfortunately, I think the only two options that will not result in missing your flight or having a stroke worrying about missing it, are staying in the airport, or going into Paris on the RER (since it's not subject to delays like surface transit is). This is particularly true if your arriving flight is late, or if you have a long delay at immigration and/or luggage retrieval (and these things cannot be predicted).

Thanks to everyone for the great replies. I guess Chantilly is out! We are arriving from New Delhi and going on to Toronto. We don't have to check in for the second flight, as we will be all checked in in Delhi. It seems that going to Notre Dame is the best option, perhaps walking along the Seine a bit, towards the Louvre (unless you have another recommendation). We should be able to reach Paris by 8:00 a.m. and spend a couple of hours.

So now, I have two follow-up questions:
1) If we get off at Notre Dame, can anyone recommend a cafe where we could get breakfast that is a bit interesting? I ask because the last time I was in that area, every cafe was packed with tourists (like us, no doubt), and it just wasn't that much fun.

2) Alternatively, is there anything to see around the Gare du Nord? Presumably, we could get off the RER there instead if it's worth it, and save a little train time.

Thanks again for all your help.

Two corrections:the RER B does have delays, in fact on a daily basis, to such an extent that regular riders had a demonstation a few years ago. But you probably wouldn't be impacted greatly. Second, you may not be checking back in, but you will go through passport and security controls.
Finally, Gare du Nord is walking distance to Sacre Coeur.

I can weigh in on breakfast. Please don't bother with a café. Since you have such limited time, just pop into any boulangerie and grab some croissants or pains au chocolat to eat on your walk. Not very French, but c'est la vie!

Also, please make sure your luggage is checked through to your final destination. It is not uncommon for airlines to make you claim and re-check, especially with such a long layover.

Thanks so much to Bets and CWyser. Super helpful, both regarding the Sacre Coeur and breakfast! Our bags are definitely checked through. It's one ticket with a stop. Thanks again!