Actually, I doubt if the time of day really has anything to do with it. Dim Mak, Dim Hsueh, or Chi Ma are really just powerful strikes done with the fingertips or knuckles in order to stop the chi from flowing. Really the correct term is Tien Hsueh, meaning striking or hitting a pressure point. There are similarities to accupuncture, but obviously you are trying to hurt rather than heal. I wouldn't say it was a myth. Just like the doctor pointed out above there are medical reasons why these types of strikes produce serious conditions like death or paralysis. Even a delayed death can even be caused with this type of attack. There also have been thoroughly documented deaths from these techniques if you were wondering....