Cenarius, once you've learned the fight, is an easier fight. As we were going though, Cenarius took us a little longer to learn. We had time for two quick pulls at the end of the night on Xavius just to see the mechanics and the fight in general, then the next day I gave my full explanation of the fight and we killed him on the first pull. Xavius feels very forgiving on normal, might not be the same on heroic though.