All the times I have visited DLP, we've always booked our restaurants (whatever time of year) through the following:
Before your departure (up to 2 months before your arrival date), call +33 1 60 30 40 50 for the Dining Reservation Service.
We've asked for all kinds of times and have found them to be very accomodating. If you're staying on site, they'll take a note of the hotel. When we arrived at the Sequoia last year, we re-confirmed our reservations and they were all there.
I'd book them 'just in case' but then I am over organised! Have a lovely time!