Sunday lunch (today) in Paris
Need to be at the airport at 2:30 so an 11:30/12 start is great.
I will look into Le Cinq at four seasons yet I believe the start too late at 12:30
will also look into start time of Le Meurice.
Our luggage may present a problem for some non hotel restaurants ...
However we are staying at Le Grand Hotel so something nearby might be an option as we can leave luggage here ...
Why not quietly stay at Café de la Paix? Finding a restaurant that serves at 12 will be hard any day, more so on a sunday, and more so on the sunday of daylight savings, when 12 is still 11 for most Parisian. Café de la Paix serves 24/24.
That said, I'm sure Le Cinq is able to serve you lunch in one hour so if you ask them. Le Meurice's gastronomic restaurant is not open on sundays. Le Ritz is.