It’s important to recognise, though, that we’re all different. Look at the veins in erect dicks in the Members Pics and you’ll see that no two guys are the same. Some have lots of veins, some not many; some have veins when clamping that bulge heaps, others don’t. So, I reckon there is no single rule that fits all. Each of us must experiment and find out what works best for him.
As for me, I can clamp for an hour or more without any ill effect except for slight blueness that goes fairly quickly after I stop. No tingling, no undue swelling, no blisters, no popping veins, etc. And I find behind the balls far more effective than in front. For best effect, I need to edge for about half the time or I lose my erection, but that’s OK. If I lose my erection, it’s as if I don’t even have it on. If I tighten the clamp just one more click, I can turn dark blue and that’s not good. So, I find myself adjusting the clamp according to the degree of erection I’ve got and how blue it all is.
All that being said, I’m a VERY hard gainer and might even give up soon. I put on good growth when I first started, but am going nowhere much now. I have noted that I produce heaps of precum, though, when clamping (could be the edging). Too much precum seems to have the same effect as ejaculation and I can go into blot for 12 to 24 hours. So, I have to be careful.