i have no experience with gentoo other than watching friends start the compile...
there is a -d switch in 'man cp' which says:
-d same as --no-dereference --preserve=link
never follow symbolic links
preserve the specified attributes (default: mode,ownership,timestamps) and security contexts, if possible additional attributes:
so maybe trying: cp -d /usr/share/zoneinfo/Australia/Adelaide /etc/localtime
hope this helps