Let's be real, when you time an LB in a dungeon should have zero effect of whether you clear the boss or not. At this point in the cycle the clear rates for dungeons on first shot should be trending close to 100%.
While mathematically it is always better to LB at the start of the fight as it gives you a chance to build back LB1...it really shouldn't matter enough to warrent a kick. Then again, you could have always been flexible and just hit LB at the start too.
