How long before the flight leaves do we need to arrive at CDG?
Most airlines, UA, DL, recommend being at the counter 3 hours before scheduled departure. AA recommends 4 hours.
If you are flying First class or have status with the airline, you will receive expedited service and can trim these times.
It depends on:
1) Where you are flying to
2) Which airline, some airlines have longer check-in times than others.
The best solution is to look on the airline website. The information should be there. If you got a confirmation e-mail with the booking, it may also be in the small print of that e-mail.