According to the theory of special relativity, it is not possible for an object with mass to travel at or exceed the speed of light in a vacuum, which is approximately 299,792 kilometers per second (or about 1.079 billion kilometers per hour). As an object with mass approaches the speed of light, its relativistic mass increases, and it would require an infinite amount of energy to reach or exceed the speed of light.
Therefore, it is not meaningful to calculate how long it would take to travel one kilometer at the speed of light, as it violates the fundamental principles of physics.