Benefit: Once per day, you can make a single melee attack while taking the total defense action. You take a –4 penalty on attack rolls when making this attack. You also gain a +4 bonus on critical confirmation rolls made while fighting defensively or making an attack of opportunity using this feat.
Does the bonus to critical confirmation rolls apply only once per day? Or is it a constant benefit?
As I read it, it's a constant effect - as long as the prerequisites are met, of course.