https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120481
--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> --- "However, if a flag refers to a “time of day” (e.g., %H, %I, %p, etc.), then a specialization of duration is interpreted as the time of day elapsed since midnight." I think it's fine for the output to be unspecified in that case, since it's not a meaningful time-of-day.
