This site states this specific instruction directly: calendar your refund deadline as soon as your order arrives.
Since the brand also frames the fullest results as building over months, this site is direct that marking the deadline immediately on arrival matters — worth doing that the same day your order shows up, not weeks later.
Set a calendar reminder the same day your order arrives, noting the brand's own 30-day minimum-use recommendation first, per this site's own six-step checklist.