A boss could expose it's weak point in 3 seconds or in 3 minutes. It's all RNG. This makes speed runs (basically all A rank runs) luck as if you'll get the boss weakness exposed enough times and within time.
Of cause you can bypass this by using a special attack while in green magic mode on the boss. But that is not something you can do over and over in a short space of time.
Of cause you can bypass this by using a special attack while in green magic mode on the boss. But that is not something you can do over and over in a short space of time.