Think I’m getting close / How long should you contract for?

In my session today I tried to contract my sphincter muscles for as long as I could at a medium pressure. It was around a minute or so.

Doing this with a rolled up towel under my hips gave the tip of my penis a vibrating sensation along with some involuntary contractions. This was definitely the most pleasure I’ve gotten about of the syn so far. However the involuntary contractions would go away when I would stop contracting.

However I’m worried that A: I may be contracting for too long? Could I hurt/damage anything? and B: the good feeling was almost entirely in the tip of the penis. Didn’t notice too much pleasure coming from the prostate.

tips/thoughts?

Lots of pleasure initially but it fades quickly. Advice?

Been using my helix syn very irregularly for about 6 months. I live with other people and usually like to make a big thing out of it when I do use it so that makes it difficult.

Normally it’ll feel amazing when I first insert it after prepping and lubing everything up. I’ll get hard instantly, produce precum, and have involuntary contractions.

Then like most guides say I try and relax. Still usually feels good at this point. Do this for about 10-15 minutes.

Here is when everything starts to fade. It’s been inside me for around 20-30 minutes and no matter what approach I try (porn + contraction or no porn/do nothing) I lose most feelings of arousal. Sometimes I’ll still produce precum but I can’t say I feel any pleasure. What should I try/do?