After beating the final boss you will have a short segment where you have to figure out a way to save your castle. During this there will be a ten minute timer in the corner. This event is rather short and ten minutes is far more than enough time to get it done, but you need to let it run down to 0 to get the achievement. Note that the timer hitting zero does nothing (hence the achievement name), so you dont have to refight any bosses getting this, and it is best to wait for the remaining time right at the end.
After the timer starts follow the pizza delivery girl into the room and talk with her, leave and follow the path to find the last heirloom. After finishing the heirloom trial, use it to go back the way you came and open a hole under the castle where a gigantic portable rock is hidden. Lifting that stone will end the game, so wait out the rest of the timer here then lift it to end the game after the achievement pops.