When setting up my latest Kickstart files for Fedora 19 I noticed that the default GNOME clock format of the clock displayed on the login screen and user's desktop and lock screens were all in 24-hour time format. I wanted to change this to a 12-hour clock format. I first came across a post that explained how to do this using dconf under the gdm user's account:
This works great and may be what some users want. However, this only changes the format of the clock on the login screen and its lock screen -- Once you log-in as a user or create a new account on the system, the user ends up with a 24-hour clock.
I then stumbled across glib-compile-schemas which provided me with a way to override the defaults provided by the settings schema. To use glib-compile-schemas I must first create a schema override file in /usr/share/glib-2.0/schemas. Because I will be overriding the clock-format value in schema id /org/gnome/desktop/interface/ I will name my file org.gnome.desktop.interface.gschema.override. It is important that the file's name ends with .gschema.override as this is required by the glib-compile-schemas utility.
Once I have defined all my overrides I can execute the glib-compile-schemas utility on the /usr/share/glib-2.0/schemas directory:
There may be some warnings displayed as there are deprecation notices for some of the keys defined by other applications. Once that was done I restarted and can see that my override has resulted in the default time format for all users, gdm included, being set to 12-hour.
Hope this helps someone else who manages systems for multiple users and likes things as automated as possible.
