def get_last_release_time(self, package_family_resource):
return <NUM_LIT:0><EOL>
Get the last time a package was added to the given family.

        This information is used to cache resolves via memcached. It can be left
        not implemented, but resolve caching is a substantial optimisation that
        you will be missing out on.

        Returns:
            int: Epoch time at which a package was changed/added/removed from
                the given package family. Zero signifies an unknown last package
                update time.