"30 day span", "30-day span", or "30 days span"
As in, "for each 30-day span, a late fee will be charged." I think the hyphenated version looks best, but is there some sort of authoritative word on that in a style guide?
Solution 1:
Style guides sometimes say different things. They are authoritative only for the people to whom they're addressed. That said, I don't see how anyone could object to 30-day span. The hyphen between 30 and span shows they are to be read together adjectivally, and the singular follows naturally from each.