If this RSVP is for a holiday or a special day(thanksgiving,christmas,valentine`s..etc) , I recommend you book a table a month ago or sooner. for a weekend table a week ahead will be just fine as well as a weekday table.
I`ve not tried this place yet , but that salad you decribed sounds same as Panera Bread`s salad. Panera has this on their menu , with walnuts , baby greens,roquefort cheese (as the blue cheese) and raspberry vinegar. strange