Light travels at: 299,792,458 meters per second. So the reciprocal of that is true for 1 meter, i.e :
1 meter takes 1/299,792,458 of 1 second. And:
1 centimeter takes 1/29,979,245,800 of 1 second. And:
1 millimeter takes 1/299, 792, 458, 000 of 1 second