Proposed resolution:

This wording is relative to N5008.

1. Modify [time.clock.local] as indicated:

   
   template<class charT, class traits, class Duration>
     basic_ostream<charT, traits>&
       operator<<(basic_ostream<charT, traits>& os, const local_time<Duration>& lt);
   

   -?- Constraints: os << sys_time<Duration>{lt.time_since_epoch()} is a valid expression.

   -2- Effects:

    os << sys_time<Duration>{lt.time_since_epoch()};
   

   -3- Returns: `os`.

Stream insertion for `chrono::local_time` is defined in terms of conversion to `chrono::sys_time`, but not all `chrono::sys_time` specializations can be inserted into an ostream, because one of the overloads is constrained and the other requires convertibility to `chrono::sys_days` (see [time.clock.system.nonmembers]).

This means the following code fails to compile:

#include <iostream>
#include <chrono>

template<typename T>
concept ostream_insertable = requires (std::ostream& o, const T& t) { o << t; };

using D = std::chrono::duration<double>;

int main() {
  if constexpr (ostream_insertable<std::chrono::sys_time<D>>)
    std::cout << std::chrono::sys_time<D>{};
  if constexpr (ostream_insertable<std::chrono::local_time<D>>)
    std::cout << std::chrono::local_time<D>{}; // FAIL
}