I dont have this method but I do seem to be able to fall in to a routine in less than a two week period and then just wake up at the same time every day essentially invariably, not sure how I do it. I dont remember it being like that when I was a kid, but at least since my military service Ive been able to get up when needed (not saying its correlated to military life, just that thats what point in life I was at when I noticed this)