do it now, i never did it on day one, it was about a month in for me as i didnt own a tape measure and even then i used my dressing gown cord which wasnt accurate as when i laid it out against kevs metal tape measure on the floor the dressing gown cord stretched!! so my starteing measurements are only a rough guide which i think is pretty close as my bra size is pretty spot on with what i got. i measured myself again last week (with a proper clothes makers tapemeasure this time!) and iv lost 3inches off my chest, 1 inch off my waist and 3.5inches off my hips to date