It's all based on circulation. Very few [words=https://shop.mattersofsize.com/products/sizegenetics-penis-extender]extenders[/words] are safe to wear unsupervised.
If it's got a noose or strap: DON'T DO IT.
Too long is relative, but you'll find that loss of feeling, blue coloring, pain and general discomfort force you to remove it. If you're sleeping you will not notice numbness and blueing, but you will most likely rip the thing off in your sleep if it's because of pain.