10 hr is plenty of time and mobilis day pass works for cdg now.

Alternatively you can rent a car for a day and go to nearby northern suburbs - chantilly etc (half hour drive) but saturday will be busy with paris weekend crowds.

There are a few Guerlain boutiques in Paris, but I believe the one you're looking for OP is at 68 Ave des Champs Elysees as someone else mentioned before, which is essentially the flagship.

The one that MSPEconomist is referring to is at 356 rue Saint Honore, closer to the Opera/Louvre.

If the Guerlain you're looking for is truly near rue de la Paix/Place Vendome (or if you have time to be in the area), I recommend Le Petit Vendome which does fantastic take-out sandwiches (no sit down) for around 6 to 7 euro. It is just around the corner from the nearby Park Hyatt. If you are sitting down (takes longer, can't be rushed), the charcuterie and tartare is superb.

The distance is not that far between Champs Elysees and Place Vendome - you could walk (30 mins), take RER (20 min), or maybe you're brave enough to pick up one of the electric scooters.

Def worth a day trip
 

Barring special circumstances (strike continuing an extra day?), it is def worthwhile to venture into the city. I've done similar day excursions in Paris twice, and both times I had a great day just walking and enjoying the city. Both times I used RER to get into Paris. Also, both times, I had my luggage short checked to Paris. I collected my bags and left them with the baggage service in 2A (I believe it was 2A). Then whatever I bought could be placed in my bags before checking in for my connecting flight. The side benefit of this is that you know where your bags are. CDG is a big black hole for bags, and extra long layovers bring additional risk. For me, it was worth it to short check my bags. YMMV.

I'm an always leave the airport kind of traveler so adding another vote for getting out of CDG. 10 hours is plenty of time.

Saturday should be much easier traffic wise. I agree with the suggestion to consider the airport bus instead of the RER only because it will take you closer to where you ultimately want to go. For food, I recommend parisbymouth.com -- great recommendations.

Plan any visit to Notre Dame carefully -- the area has many barricades up and many streets are blocked. I think it can be seen and approached from across the Seine, but it might be best avoided on such a quick trip.

There's no way I could keep myself from heading downtown on such a layover -- I find I can cover a great deal of Paris in just a few hours. I'd get the Guerlain errand out of the way first and from there walk down to Pont de l'Alma (find a cafe for lunch (croque monsieur pour moi), and then walk along the Seine from Pont de l'Alma to Concorde, through the Tuileries a bit and then up to Place Vendome and the Opera, and then over to Gare du Nord to catch the RER back. Stop at a small boulangerie for some pastries to go. If you want to splurge, stop at a shop on Rue St. Honore and send in the VAT refund form when you return to CDG I was just there last week and this has me longing!

Echoing the others... totally enough time, especially on a weekend. Enjoy!!

I’d get out of the tourist trap that is Paris.

Go to Chantilly and get fat on their cream. You’ll never be the same, and it won’t add appreciably more travel time to your excursion. Just Uber or pay 80€ and rent a car.

If you take the RER-B from the airport, wait for the express train. It's not faster, but you avoid stops in all the stops in the sketchy neighborhoods north of Paris. Trust me on this. It's worth the wait.

There is also the RoissyBus, which I used on a layover of similar length when it turned out the RER was affected by a strike.

Another vote for doing something in Paris - I've gotten into Paris on five-hour layovers no problem.
For something aviation related, if you haven't been, you may want to check out Le Bourget (Musee de l'Air et de l'Espace).
If you didn't have to be in Paris at all, and wanted to see someplace outside, I would recommend Compiegne, which I did on a 10-12 hour layover, but may be hard to do it justice if you also have to be in Paris.

The Guerlain boutique on Champs Elysee is right next to Marriott, which is right next to Sephora, in other words Marriott is between Sephora and Guerlain. Next to Sephora is L'Occitaine, which shares space with what I recall is Pierre Hermes that serves decent food. If you get off at metro stop Etoile and walk away from the Arch, its la 5 min walk to Guerlain. After that if you keep walking you will come to the obelisk. Concord and Tuileries and Louvre. Turn right on the street just before the Pyramid, you will hit Seine and Musee D'Orsay. Right after Guerlain, few doors down you will see the Champs branch of Galleries Lafeytte, a fairly recent addition to Champs.

Airport to Marriott or any where in the city, really, the taxi is fixed price at 50 euros, same on the way back, if cost is no concern There is also Air France bus (old name) that will bring you to Ave Carnot, which is is one of the radial streets around the arch., Just walk to Champs. It may be a cheaper option at around 40 euros for a round trip. You take it out side the terminal and get dropped back at the terminal.

It is really worth it going in to the city.

12 years ago had a 7 hour layover in Paris, which was intentionally booked, so we could see the city. Took the train and got off at Notre Dame. Had breakfast at a cafe and walked along the river to the Eiffel tower, before taking a cab back to the airport. Not everyday you can see Paris for $50.

In July I paid 58 Euro for a fixed rate taxi from central Paris to CDG. I think the 50 is out of date.

Fixed rate remains at 50-55 Euros. 58 Euros is not a legitimate fixed rate, especially because taxis aren't allowed to charge extra for luggage or previous additional charges.

What do you call central Paris? Because such term is not widely used here.

You went to either the left bank or the right bank. Left bank is 55 Euros, Right bank is 50 Euros.

From PHV (Right Bank) to CDG T2 Sheraton in a taxi ordered by the concierge. I requested AC and to be able to pay with an AmEx card. I was told that this is the fixed rate.

I said central Paris because AFAIK it should be tyhe same rate from all of "downtown" Paris and I hadn't thought that my hotel choice would be anyone's business but my own.