It's okay you can sleep with it on, just make sure it's not too tight. I used to sleep with two shaft collars on my balls with a cable clamp in between as a spacer while wearing a sock underneath. I'm thinking about starting up again, I'm currently looking at this item that dickleaker mentioned...
It looks cool because you can wear it as a cock ring for after girth and sleep with it on. It's also a ball stretcher so you'll be keeping your balls stretched as well. I was also thinking about getting the ''fatty doughnuts'' from that site too so I can add the rings to my balls to increase the stretch. Here's the link to the six pack..
I also like the neoprene ball stretch as well, the only thing with the neoprene is it might be harder to clean after a night of ball stretching unlike the other silicone products.
Ball stretching while you sleep is a great idea because you usually won't have any other time to wear this stuff because your doing other pe during the day.
Personally I would NEVER do any form of Penis Enlargement while asleep. Honestly, a saline scrotal inflation sounds safer than wearing a stretcher while you sleep to me.
You should have 16 or so waking hours per day to wear a ball stretcher and do Penis Enlargement. Why use the 1/3 that is most dangerous and supposed to be restful?