https://gcc.gnu.org/bugzilla/show_bug.cgi?id=119141
--- Comment #9 from Jonathan Wakely <redi at gcc dot gnu.org> --- No, that's absolutely not what it means. The original author of that wording and the reference implementation of chrono is quoted saying what it means at https://cplusplus.github.io/LWG/issue3090 "This refers to the compile-time conversion factor to convert Period2 to Period. If that conversion factor is not representable as a (reduced) ratio<N, D>, then the constructor is SFINAE'd out. This might happen (for example) converting years to picoseconds." If ratio_divide<Period2, period> cannot be calculated, e.g. because it overflows intmax_t, then the constructor is not usable. It has nothing to do with the runtime values that must be converted, because that's not possible.
