You character breakfast will be on the first sea day after your first dinner at Palo. So, if you have APLAPLA your breakfast will be on Sunday morning (even on the Western as you don't dock at Key West until after noon), if you have LAPLAPL it will be on Monday and if you have PLAPLAP it will be on Thursday. If you have Main dining the CB will be at 8:15 and if you have Late dining it will be at 9:30 (times are estimates...I don't remember exactly).
But...you won't find out your dining rotation until you get to the terminal so there is really no way to know in advance which day it will be for you. If you are trying to figure out which day to book Palo brunch without it conflicting with your CB don't worry about it. Just book the latest Brunch time and you'll be fine. Then, on the off chance they end up on the same day, you can go to the CB and just have something light (the food is not great at the CB) and then head to brunch later.