Paris Layover

Yes, you ill have to go through Schengen Immigration regardless, since your connecting flight is to inside Schengen Zone.
Are just wanting to look at the Eiffel Tower, or actually go up? If you just want to look, I guess you can play it by ear knowing you have to start back to the airport by noon. Consider that if you want to see it up close, it is more than just the 45 minute ride into Paris. You will have to take at least another Metro connection to et close.
How many are a few friends?

thank you! We were thinking of just looking and not going up. There are a total of 4 of us.

It will take AT LEAST one hour each way. I would not do it as it would be too stressful for me.

Hmm 6 hours. Minus deplaning (hopefully not from the back of the plane), walking to Passport control, getting through Passport control, walking to the RER station. Could take an hour if there are a lot of international arrivals = 5 hours left. Buy your tickets, take the RER into the city. Transfer to the Metro. Get off at the correct stop, walk to the ET: a quick 1 1/2 hours if there is minimal wait for trains. 3 1/2 hours left. You need the same amount of time to get back to CDG, and need to be in the airport 2 hours before your flight to Naples and get through security and to your gate. In this scenario, you have 0 time to actally look at the ET for a couple of minutes, never mind going up it.

What CJean said. If you do the math, it just isn't worth it IMHO. Too much stress and a very real risk of missing your connecting flight. I would hang with your friends at a restaurant or bar at the Airport.

Absolutely not worth the risk. 7 hours is the consensus for the minimum time necessary to venture into the city. And even that depends on several variables, not the least of which is the work being done on the RER B, causing delays and detours.

I am too risk averse to do it but I do know of a family that did a trip into central Paris successfully during a short layover. When the mom of the group reported back, she said that the two keys to her success was that their flight arrived 45 minutes early checking into the ongoing flight and having their boarding passes. She was also ready to turn around at any step of the way if it started to look like they were not going to make it. They were risking having to buy last minute tickets back to the US. You are only risking tickets to Naples. Plan on 3.5 hours of travel and passport control time upon arrival and having to be back 2 hours before the flight leaves. That's 5.5 hours. You would have just enough time, assuming your flight arrives on time, to pop above ground and look at the Eiffel Tower and then head back. The family I mentioned went to Notre Dame walked around a for a couple of minutes, saw the Eiffel Tower from a distance and then headed back to CDG. They had 7 hours for their scheduled layover but then again they had/wanted to be back at CDG 3 hours before their flight departed.

you could take a cab to Trocadero for 55 Euro and have him wait for you and pay the waiting time and 55 to go back. Perhaps make the decision once you are through immigration -- although if you don't leave the airport you can do a correspondence which means short immigration lines as it is done airside. Then you end up with lots of time at the airport but reduced hassles on immigration. You could take the RERB to Denfert Rochereau and then transfer to the 6 metro to Trocadero and reverse that going back for 23 Euro each. Get two tickets each CDG/Paris from machines at the RER station.

If you leave the airport you will have to go through the regular immigration lines; it took us 2 hours from landing to being through to the luggage area after our flight in April. Our entire line was slowly fed through a single automatic immigration gate that read our passport -- and then we had it stamped by an agent. It was the longest wait we have had at immigration. Sometimes we hve been through in 15 minutes. On average it takes about an hour. If you. had our experience you would not want to leave the airport.

Any time you risk something like this you run a risk -- stuff happens. Twice this trip we have had metro lines shut down for various reasons and that can delay things an hour or so -- demonstrations, someone left a bag on the train and the drill is to call the bomb squad, someone fell on the tracks. Any little thing can hang you up so you need a plan B if you do it this way. So you need to be comfortable with rebooking to Naples if something weird happens and you miss the flight.

Going through security when you get back get take an hour. It is at least an hour to and from the city. You can do the math especially if your immigration process is as lengthy as ours.

I actually know someone who did this on a seven hour layover and missed their flight.

And the airline was not sympathetic I wouldn’t risk it

Rather than sit at the airport thinking about the potential opportunity I would take the easiest and fastest means of transportation into the city. Be ready to adapt accordingly. Hope it works out.

Consider you will be jet-lagged which can result in missteps in the best of circumstances. I would not want the stress of your plans with the short time you have from deplaning at CDG to checking in for your flight to Naples.

Make plans for a future trip to Paris that will allow you to absorb its sights rather than glance at them in a "Been There, Done That, Bought the t-shirt" manner.