I was able to fix panel clock issue by removing 'indicator-datetime' package. I saw a com.canonical.indicator.datetime.gschema.xml file under /usr/share/glib-2.0/schemas/ and thought probably that is conflicting with org.ayatana.indicator.datetime.gschema.xml when "/usr/lib/x86_64-linux-gnu/glib-2.0/glib-compile-schemas" /usr/share/glib-2.0/schemas runs.
@franksmcb, could you please check and confirm if this works for you?