EXAMPLE: 13 pounds for 1 hour vs. 15 pounds for 45 minutes.
Great question! Unfortunately I don't believe I can answer it with any definitive single suggestion. The weight and time variance really isn't that much of a difference. My personal feelings and training protocol have always been instinctive. The body adapts to the stresses and environment after a period of time. So I firmly believe variety and change help prevent that from happening. Constantly forcing your body to adapt to new or different stresses in my opinion a good thing. That's not to say you shouldn't have a structured routine. Only that you shouldn't get stuck doing the same thing for several weeks or months at a time.
The goal with penis enlargement is to change the cellular structure of penile tissues via stress. Stretching the tissue anatomy within along with forcing more blood into your penis will promote hypertrophy (cell enlargement), and hyperplasia (cell multiplication / division).
To achieve this the stress has to be sufficient to cause these cellular changes to manifest = growth.
So constantly shocking all these tissues is the goal. Sensing or determining levels of stress that trigger growth is very intuitive. I personally know that I have accomplished this when my penis is somewhat sore (not painful) the day after a extended hanging session. Additionally my sphincter muscles are sore too!
These are tell tail signs you are stressing the penile anatomy sufficiently. Make certain you are giving your body all the necessary nutrition it needs to help in the repair / recovery process. A diet with quality protein, along with supplementing with a high quality vit. C (no tablet - gel cap only) around 2000 - 4000 mg per day is advised.
With all that I have said above, use a variety of hanging angles and stretching techniques like fulcrum & bundled twists. These type of exercises really stretch and stress the penis! Couple that with a pumping routine and you will be at optimum stress levels that encourage growth!