Quite possibly it won't. I assisted in many surgical cases where ribbon has become stuck in the intestines causing a blockage, or worse yet, cause sepsis by sawing through a portion of intestine. I have seen it go anywhere from a couple days to a week or more before the cat started presenting with symptoms. The best bet on something like this, is to have the Vet examine him to be safe. Unfortunately for cats, while string and ribbons look like something fun, they can't vomit them back up because of direction of the barbs(filiform papillae) on their tongues - so everything goes one way...down.
Some things that you may see resulting from the ribbon ingestion - lethargy, lack of appetite or unwillingness to eat hard food but still drinking water, vomiting, third eyelids coming up partially over eyes, some will be tender when picked up.
Let me know if I can answer any questions regarding this for you. I will do whatever I can to help.
Medical emergencies should been seen by a Veterinarian immediately.
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Bonuses & feedback are greatly appreciated :)