LC_TIME portability (and other locale settings)

It seems that Linux and FreeBSD (at least) have different notions of how presentation of time is implemented in different locales (LC_TIME), notably but not entirely in how the hour of day is presented (12 hr am/pm style or 24 hour). Linux (as seen on recent Fedora & Ubuntu): env LC_TIME=C.UTF-8 TZ=UTC date --date 22:22:22 '+%H %T %p, %r, %+, %Ec' ; env LC_TIME=en_US.UTF-8 TZ=UTC date --date 22:22:22 '+%H %T %p, %r, %+, %Ec' 22 22:22:22 PM, 10:22:22 PM, %+, Fri May 17 22:22:22 2024 22 22:22:22 PM, 10:22:22 PM, %+, Fri 17 May 2024 10:22:22 PM UTC FreeBSD: env LC_TIME=C.UTF-8 TZ=UTC date -v 22H -v 22M -v 22S '+%H %T %p, %r, %+, %Ec' ; env LC_TIME=en_US.UTF-8 TZ=UTC date -v 22H -v 22M -v 22S '+%H %T %p, %r, %+, %Ec' 22 22:22:22 PM, 10:22:22 PM, Fri May 17 22:22:22 UTC 2024, Fri May 17 22:22:22 2024 22 22:22:22 PM, 10:22:22 PM, Fri May 17 22:22:22 UTC 2024, Fri May 17 22:22:22 2024 My questions are: Is there a standard that defines presentation for various locale specific settings (like LC_TIME)? If so, where is the standard documented?