The time selector on start date, end date, due date and reminders doesn’t follow the 12hr time format value set in the settings. Only the date time being displayed follows it but not the date time used to set these values. Relative dates should also be able to show 12hr formats for setting time.
Users should be able to set 12Hr as a separate option where everything is done in 12hr. Also, admins should be able to set the time values as defaults. The current display date & time is not configurable as server defaults.