it seems that the latest Sierra update breaks the 24 hour versus AM/PM usage on FileMaker Server 15 Admin
Cannot say if it is a Safari issue or Sierra issue.
Anyway Server Admin started to show/use am/pm instead of 24h settings by itself.
Checked clock settings in System Prefs but no joy.
Only remedy i found was to start using local language and local regional settings in Sierra.
English language and local regional settings not sufficient.
Hope this helps