It does not take even a moment for the Lord to kill any powerful demon, including Hiranyaksa. The Lord could have killed him long before, but He allowed the demon to display the full extent of his magical feats. One may know that by magical feats, by scientific advancement of knowledge or by material power one cannot become the equal of the Supreme Personality of Godhead. His one signal is sufficient to destroy all our attempts. His inconceivable power, as displayed here, is so strong that the demon, despite all his demoniac maneuvers, was killed by the Lord when the Lord desired, simply by one slap.