Your wearing period should be based on the type of scrotum stretcher you use. For example, you shouldn't wear a metal stretcher for the same amount of time you would wear a leather or silicone stretcher because metal is more intense than the others.
Regardless of the type of testicle stretcher, there's no definite wearing time. We advise that you wear a metal stretcher for only three to four hours daily. You can remove it earlier if it hurts and go a bit longer if you find it comfortable. Also, you can wear leather ball stretchers and other gentler variants for the entire day as long as you don't feel discomfort.