I just made a late breakfast reservation at Boma's for our last day. The CM on the phone told me the latest is 10:45. Not sure about the animals though.
I had heard that you can't see the animals from the actual restaurant but someone who has been there could better tell you.
And the earlier the better when it comes to animals- that's what everyone will tell you about the safari at AK too- animals are more active in the morning when it's cooler- if you go at 10:30 or 11 almost midday, you'll see less.
I always hate going to the end of buffets too- the food has been out longer. Of course, I have gotten food poisoning TWICE from eating late at buffets so maybe I just have bad luck
You can't see the animals from inside the restaurant. You have to go outside and walk around the viewing area. The hotel is made that you can go to certain places and see the Savannah. You will see the animals from there. The Breakfast is one of the best I have ever eaten at Disney. They have a omlet station and their own juice blend.