Change Organization Time/Date Format

We've just set up a new organization, and all of the date formats are defaulting to US mm/dd/yy rather than our country default dd/mm/yy (Australia). 

There are is a dizzying list of locations that date formats can be changed, but it's both annoying to change in *every* app, and a bit unprofessional for users/employees to have to do the same.

Id expect there is a single location this can be changed, but I can't seem to find it.