We've stayed at CSS three times in a row and have had flights that leave between 4 and 4:30 pm. Unfortunately the shuttle leaves VERY early in our opinion, at around 11 or 11:30. BUT we always leave on a Saturday or Sunday. We're able to eat breakfast, but the rest of our morning is spent packing, turning in our beach towels, buying pictures, checking out, etc - and then it's time to go!
The shuttles aren't on a predetermined schedule, they will leave according to your flight time. If it means you are the only ones on a shuttle then Couples will arrange a shuttle just for you. You will be notified a couple days ahead of your departure regarding check-out procedures and your shuttle time. Generally you leave the resort ABOUT 4 hours before your flight departure time so as to have you arrive at the airport 2 hours prior as the airlines require.