The boss has more power than 6min. You just need to get more powerfull. Keep in mind it's not made to rush so fast. Normally u have enough time to gain the needed power to defet the bosses.
And since the mod don't work for boss stages and other stuff like the dungeons, you just need to get more power and have the right setup of hero combinations.
how you gonna abuse it, its not working on the final bosses, you gotta power up your character somehow at this point to clear the final stage of the chapter