This is a bad example, since "Would you mind waiting two seconds" might mean 90 seconds. But that doesn't mean you can say 2 instead of 90 in the general case.
I readily concede your astute counterpoint but what I'm suggesting is that unlike actual cardinal numbers, words like "couple" are much more likely to be used euphemistically than literally, when in adjectival phrases. But in the noun form then I agree it means "a pair" and no more.