I've heard that doing it in the morning is best before you eat so your 'fasted' sp to speak. Personally I can barely mumble before I have a coffee and couldn't bare doing cardio to early LOL. I do mine in the arvo's or evenings, usually after my workout, but not directly after, about an 1 hour to 1.5 hours later. My work hours are all over the place these days so I just fit in what I can anf watch what I eat.