Originally Posted by
ajeleonard
Yes, plenty of time to take the RER in, it can even drop you right at Notre Dame
Not sure I agree.
You are not clear as far as where you arrive from and where you are going to.
If it includes any form of immigration then all bets are off.
You should also be back at least 60 min before the flight assuming you have a boarding pass and do not need to check any bags.
Be realistic; you will get to Notre Dame, look around, grab a quick bite and then have to head back.
Buy a day trip with RER so you do not need to buy a ticket on the way back.
When you come out RER in Notre Dame, walk a little along the river heading towards the west and you can get a glimpse of the Tour Eiffel.