depends on many factors. How well dehydrated you are, your build and physiology, what kind of work out you are doing etc... I know after an intense work out with weights I am very impressed with how my muscles look but they will loose the high amounts of blood 1 to 2 hours after the work out, I can look 20 lbs heavier at the end of a work out than I did at the begining of the same work out.
45 minutes