You can soak your greens in water and they will stay crisp for a day or two without refrigeration. If they've been laying out and have wilted or have gotten dry spots, there's not much point in saving them.
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The smell and appearance of foods will usually tell you if they are fit to eat. Does it have mold on it? if yes throw it out. Does it smell bad? If yes throw it out. Is it appealing ? If no throw it out. Does it look like something you want to put in your mouth? If not throw it out.
I personally would not recommend eating collards after 5 days. 2 days at the most.
When in Doubt throw it out!
After 2 hours of being removed from the heat, they should be refrigerated if you want to keep them to eat later.