For how long can the human body withstand rubbing one out every five minutes before dehydration/stress causes the body to black out?

Well, if we make use of the peen factor, the equation that states v=mrtu²dff³∛df² then we can input the numbers that you have mentioned to calculate that your dehydration rate will be at an astounding 1.3x10³ mega joules per square kilogram of body mass of your peen and a stress level of 74635025436957² Newtons per square gigagram of peen mass. Dividing these numbers gives us 94, proving that you can in fact do about 53784 before the body disintegrates from using its body mass to go through the process of rubbing one out.