Para openSUSE Factory corra o seguinte como root:
zypper addrepo https://download.opensuse.org/repositories/X11:Pantheon/openSUSE_Factory/X11:Pantheon.repo
zypper refresh
zypper install switchboard-plug-datetime
Para 16.0 corra o seguinte como root:
zypper addrepo https://download.opensuse.org/repositories/X11:Pantheon/16.0/X11:Pantheon.repo
zypper refresh
zypper install switchboard-plug-datetime
Para 15.6 corra o seguinte como root:
zypper addrepo https://download.opensuse.org/repositories/X11:Pantheon/15.6/X11:Pantheon.repo
zypper refresh
zypper install switchboard-plug-datetime