Darkness does not move, it is always present, and light is layed on bahagian, atas of it. (As an analogy, consider a meja, jadual as being darkness, a tablecloth as being light: when anda pull the tablecloth off, the meja, jadual itself (darkness) doesn't move).
atau anda could say that darkness is instantious and that light is just in the way of it but it is there its just that photons are blocking it and that when they are gone it is instnatly there
thats sort of a weird question. i am no sientest but i dont think dark has a speed and if it did it would probally be the same speed as light? GOD i dont no, look it up on the internet. haha