Proposed resolution:
This wording is relative to N4741.
Edit [time.duration.nonmember] as indicated:
-1- In the function descriptions that follow, unless stated otherwise, let CD represent
sthe return type of the function.[…]
template<class Rep1, class Period1, class Rep2, class Period2> constexpr common_type_t<Rep1, Rep2> operator/(const duration<Rep1, Period1>& lhs, const duration<Rep2, Period2>& rhs);Let CD be common_type_t<duration<Rep1, Period1>, duration<Rep2, Period2>>.
-10- Returns: CD(lhs).count() / CD(rhs).count().