My favorite time to book a PS for lunch is the first available PS. I'm not sure what time that would be at CP, but probably 11 or 11:30. That way, you're booked first thing, and aren't waiting for other diners to finish lunch. When we booked the first available lunch PS at CP, we were seated right away when it opened, no waiting. Love that! We didn't mind the early lunch, because we had a light in-room breakfast, and were hungry by then: )
Also, when I booked the first available lunch PS at Coral Reef in Epcot, we were also seated just about right away, no waiting for others to finish, and were able to ask for a table by the fish tank, and got it. Did the same thing at 50s Prime Time Cafe. I highly recommend this technique if you have a light in-room breakfast to save time (get into the parks early) and money.
This trip we're doing both princess breakfasts so we won't be doing those early lunches.