GNOME-Shell "MultiClock".
It was made because I need to reference Perth time (UTC+8) all the time.
CONFIGURATION
Click on the displayed "alternate" time; selection from the dropdown is saved for future logins.
INSTALLATION
cd ~/.local/share/gnome-shell/extensions/
git clone https://github.com/mibus/MultiClock.git MultiClock@mibus.org
LICENSE
This extension is distributed under the terms of the GNU General Public License, version 2 or later. See the LICENSE file for details.