Tested the dbus command and it works fine when executed as root (and also as 'su user -c ...', so no idea. I did not test to execute it as service.

About worldclock installment:
please read from here and download the deb, extract it and simply replace /usr/bin/worldclock. Should do the trick.


--edit
just checked with file in /etc/event.d and indeed it fails with "Failed to open connection to "session" message bus: (null)"
But simply preceeding with run-standalone.sh works.

Please note the escaped " around worldclock.