We're doing a 2:30 ceremony at Sea Breeze Point followed by a 6:00 at Chef's Domain in Citrico's. Chef's Domain only seats 12 people, and the only seating is at 6:00, so that won't work for a party of 18 who want lunch. However, I've seen brides do lunch at Citrico's (which is normally closed for lunch) - there are quite a few places where you could have a private lunch if you didn't want to just book a table at a restaurant that's open for lunch anyway. There are rooms at California Grill, Jiko, Narcoosee's, The Wave, and some other restaurants that you could book for a private reception for lunch. The real difference between booking the reception at a restaurant that doesn't normally serve lunch is that there are food and beverage minimums that must be met, but with a party of 18 people, that shouldn't be too difficult.
Hope that helps!