I agree that if you’re going to use an extender a vacuum cup is preferable to a noose type. Though I have noticed if you don’t put the vacuum cup on just right, which is tricky, it can cause one side of the glans to grow more than the other and reduce your symmetry. Maybe that’s just me?
I got an extender and plenty of extra rods, but it’s just too much hassle to wear for long periods of time and it’s difficult to keep the area warm. It doesn’t help that the standard base ring doesn’t allow much girth and having an erection into it turns it into a very tight cock ring for people approaching and beyond 6” circumference. Larger girth set ups are available, but expensive for a tool I don’t really like using anyway. The cups that are used for the vacuum types have limited size too. It’s a very tricky thing to get a flaccid glans past a silicone sleeve because the cup behind the sleeve is too small for the erect glans. And the sleeves tear easily. It’s all very tricky.
To answer the original question, when stretching you can reach a point of fatigue where the penis does not experience tug back. If you’re passed the point of fatigue there will be no tug back immediately, if you are not passed it the penis will retract and be harder to stretch back out. So taking breaks before the point of fatigue could make the whole exercise more difficult.
I’m skeptical that the fatigue should be the goal of stretching myself, since in my experience going past the point of fatigue, while not causing immediate tug back, causes a significant (.5”) reduction in erect length the following days.
Starting: 7"bplx5.2" 2017 (shrunk from disuse)(originally 8"bplx4.5", gained to 9"bplx6")
Current: 9.0"bplx6.125" 2020
Goal: 11.5"bplx7" 2021.