"As soon as it starts to hurt" is not some hopelessly complex and useless standard that involves delving into philosophies of subjective pain sensation. It is actually obvious and easy to follow.
Use it, but when it hurts, stop.
Use it, but when it hurts, stop.
no amount of pain tolerance will help you if something is broken.
you WILL feel it. simply stop when you do.
it's not a hard thing to grasp.
Sleeve tattoos but needs an IV? “Oh, I’m not good with needles, you need to sedate me first.”