Meh.
It's a difference game. Truly, score shouldn't be based off of the time you click, but the difficulty of the spotting itself. By making it about speed, you encourage mistakes in clicking, especially in later levels where, indeed, even a pixel off can be a difference between you getting it and not, and when, after a bare couple seconds, the score gained is only 10, while the score for losses is -100, it sensitivities the player TO actually find it quickly.
Plus, it takes too long for the difficulty to ramp up, and the loss of lives, and game overs, disinsentivize playing further.