At what point is a shed considered a "stuck" shed?

If you have to help the snake remove the skin, what is the best way to do that (beyond letting them crawl through a damp towel in your hands, because mine just sits there)?

How long do you usually wait and let a snake try and figure it's skin removal out by itself before you physically step in (as in, you've put damp paper towels in hides, etc.)?

What do you recommend for accurately measuring humidity that isn't going to cost an arm and a leg but is still quality?

Sorry if any of this has been answered a million times, I tried my best to get as much info as I could from existing posts.