Hacking missions can appear on the map or when you intervene during a mission and consist of moving in a sort of maze to reach the exit cell. Story-related hacking missions are not timed while the others are, and you can see if it's timed by the bar above the maze.
This achievement can be unlocked naturally with the highest level missions, but you can unlock it early: you can navigate through the maze and stay on the exit cell until the last seconds. When the bar is almost empty, complete the mission to unlock the achievement.