I just checked a couple of my guidebooks and they both show CM closing at 11:30am. It doesn't say when the last seating is though. Sorry I could'nt be more help.
We go for a brunch every trip and they always give me an 11:15am seating.
This is a fabulous time to go as almost everyone seems to be leaving and you get lots of character interaction with Mickey and Minnie. My kids love to sing and wave their napkins in the air too!
We have a 10:15 breakfast for July. I just hope the food is still fresh at that time. We have never done one that late but thought it would give us time to sleep in a little and then maybe we could skip lunch.