SIM cards purchased in CDG airport upon arrival activation time

I have activated new SIM cards in a couple of countries (but not France), it usually takes just a few minutes.

The salesclerk in the Relay shop might not have enough time to install and activate the SIM card for you. Some new phones require a nanoSIM, which is smaller and has to be cut to fit your phone. You can do this yourself, though, if you have a pair of scissors.
Or, if you don't need your phone right away, you can go to an Orange boutique and buy a SIM and have them do everything for you. Just try not to go when the store first opens or at lunchtime. Google store locations near you.

I never leave the store/kiosk until I have made a call using the new SIM card - normally I'll call the clerk who helps me set it up. I always ask to set up the language as English, but seem to always get something (like a call telling me my time is running out) in the local language.

With no prior experience we installed an Orange SIM in the Iphone in just a few minutes (the clerk in the Tabac stand at CDG had no interest in assisting; but it wasn't an Orange storefront). The included multi-language instructions and drawings were easy to follow. It "launched" itself immediately and sent us a confirming text.

I've done it at a Relay store at CDG and the clerk even helped me make sure it was activated! Your experience may be different. In any case, there is no 48-hour waiting period.

Thank you to each one of you for your helpful comments.
db

We initially purchased SIM cards at the Relay store in CDG but within a day went to an Orange store and bought new SIM cards. The cards from the Relay store (can't remember the telcom provider) were close to useless in terms of data coverage. We use our phones primarily for data and we were frustrated beyond belief in a few short hours because of the inability to load websites and especially maps for navigation. We rarely got more than 1 -2 bars of coverage. Once we had the Orange service we never had a problem. If you can manage without a phone until you get into the city I'd make the Orange store one of my first stops. Just make sure you find the one closest to where you are staying before you leave the States and make sure they will sell SIM cards. The first Orange store we went to in the Marais doesn't sell SIM cards (and had a large sign on the door stating that). If you can, try to find an Orange store away from tourist attractions - the store on the Champs d'Elyse is always busy but have lots of English speakers. Other locations are not so busy but English might not be as prevalent.