Time Debate

Since you and your sister fundamentally disagree, I suggest you each leave for the airport separately therefore each does what she wants. When two people are traveling together with different requirements about getting to the airport, the best thing to do to keep peace is to meet at the gate. I would leave one hour for a taxi & arrive at 8am but I am not your sister!

Well Google says that at 6am it will take 30 minutes to 1 hour. and at 7am 45 minutes to 1.5 hours (rounded a bit).

6 am + 1 hour + 2 hour pre flight = 9am (go drink coffee)
7 am + 1.5 hours + 2 hours pre flight = 10:30am (if everything goes perfect this works)
So I would leave no later than 6:30am (to be honest, I would leave at 6am and have coffee)
Why 2 hours pre-flight .... because Chucky D. is a miserable airport.

If my sister didn't make it on time, there is no way I would leave without her, so for me arriving independently is not an option.

Yes, separate taxis would keep the peace, at a price. But you may not need to get to CDG as soon as you think, two hours before flight time ought to be enough. France and Austria are both in the Schengen area, so this will be a "domestic" flight within Europe.

I’d split difference and depart 6:30

I shared this post with my sister, (the one who is willing to slide into CDG on two wheels), and we decided it would be prudent, as well as cost effective, to travel together and leave at 6am.

We have traveled to Europe together MANY times since 2009--sixteen or seventeen times. I have lost count.
I have always been planning and logistics; she has always been the navigator.
Perhaps in my old age (64) she is beginning to question my ability. Nah, she stopped minding me when she was in the fifth grade, so it is probably just 'push back'.

(6 am it is)

Thank you for your suggestions.

This is an internal flight, so they won't let you check in more than two hours before. Leaving at 7 to check in at 8 will enough. If you are still uncomfortable, try 6:45.

Traveling to the US you would leave at 6 to catch a 10 am flight. I am very conservative about air travel -- would rather read a book and drink coffee at the gate than miss the flight -- even I would leave at 7 for this flight which would get me there two hours ahead which is plenty for a domestic flight. (well maybe 6:30 --)

My husband and I have had this battle for all 50 years of our marriage; after a couple of close calls where we barely made a plane as they closed the door, he has agreed that the person most nervous about this should decide. So we always get there the recommended time.

Leaving at 7:00 is fine. You could take the RER. While I love cabs, during morning work hours RER will get you there faster as and it sort if cool to see the commuters.

For a flight to Vienna, 7 is fine. Maybe 6.45 if you want to play it safer for the sake of compromise.
I would not want to mess with the RER, as it is inconvenient to catch it from the Champs Elysées area and possibly very crowded on weekday mornings.

I’d leave at 7am, as others have said.

We flew out of Paris last Tuesday. We had a 9:10AM flight to the US and took a Bolt at 6AM from our hotel in the 17th. It took us 20 minutes (yes, 20 minutes) to get to CDG, which was a ghost town. We checked bags and were through passport control and security in 30 minutes.

I think 7AM is more than enough time.