Some cells are incorrect to throw you off as a red-herring distraction, but the final answer is always legit.
The time limit was experimental, but you can beat it if you restart the puzzle a few times, as the final answer does not change. The time limit is a superficial obstacle but I do need to make it slower, as it makes players panic.
In the main Menu, press the "Ninja" button, to get to the second half of the game. I may add a password system if the final game gets to be too long.