See Mods Admin for instructions on how to install a Mod.
Usage
Once installed, you will see it under "Admin > Modules" (tiki-admin_modules.php):
You can assign a this Module to a lateral column (See Module Admin page if needed), or you can include it within a wiki page, using the PluginModule.
The assigned module looks like this:
By default it shows your local time. but you can change it to the time of any country from the drop down list (shifted to Argentina time two minutes after the previous image was taken):