Thanks for being honest. It is pretty random. The knights fight autonomously and the attack chains thus have a random length that you can't influence. You basically bet on how long the current attack chain is going to be. The longer you wait before activating your buff, the higher the buff is going to be. On the other hand the earlier you activate it, the longer it will be active until it is reset at the end of the turn. It's basically gambling, but it has a strategic component because you can react to the enemy's buff activation decisions.