While I basically agree with bigluke39’s main point (you never need to stretch at 100% when using an ADS), I would put it differently. I don’t think there is a hard and fast rule about what percentage of stretch you should be doing. Everybody’s body is a bit different.
So here it is. Two things.
The first is the most basic and the most important: if your body is sending you pain signals it is a red flag; if it sends them consistently it’s a big red flag - maybe even a flashing light.
Please read everything you can about Physiological Indicators (PI's). You will never help your PE cause by injuring yourself. That’s main thing and it applies to all forms of PE.
The second thing is in regard to the use of an ADS.
If you are using this as your primary form of PE consider doing some hard core stretches first. You could even use the PenisMaster and stretch to 100% of your BPFS, but only do this (or your hard core stretches or whatever) for ten minute or fifteen minute sets. Then let it relax for about 5 minutes (and remember to give it more heat - you are using heat, right?), and then repeat. Do three sets (at the maximum). When you’re are done with your intense stretches, then use the PenisMaster and stretch as far as you can go without any discomfort. Use the minimum amount of tension to extend it as far as you can - less than you are fully erect.
The idea with an ADS is to keep it stretched out just enough so that it heals in an extended state. You don’t need very much stretch with the ADS, and you should basically be able to wear it without noticing. If you begin to feel discomfort, or any coldness, and certainly any numbness or tingling, or if it becomes dark purple and cold, take it off. Massage it a bit, get the blood flowing and put the device back on, but back-off the tension. Even if it’s comfortable and warm (good blood flow, etc.) you should take it off every hour or so and massage it a bit, promoting warm blood flow.
PE isn’t the practice of beating the living hell our of your dick and forcing it to grow. If you try that, it will rebel and you will actually go backward; the penis will recoil and try to protect itself and send you pain signals.
What you really want to do is remember that this is living tissue; put manageable heavy stress on it for short periods of time and then use the ADS to keep it in an extended state while it recovers from this stress - just enough to keep it extended, but not enough to be stressful.
See if that approach doesn’t work better.