The NTP ebuild says: "The way ntp sets and maintains your system time has changed. Now you can use /etc/init.d/ntp-client to set your time at boot while you can use /etc/init.d/ntpd to maintain your time while your machine runs" That seems to indicate that ntpd and ntp-client should both be started. However, the wiki says: "Make sure you are not running ntp-client" http://wiki.gentoo.org/wiki/Ntp#Server_2 I think the wiki is correct.
/etc/init.d/ntp-client doesn't keep anything running - it runs ntp-client, which sets the system time once and then exits, leaving the NTP ports free for ntpd (or a different NTP daemon) to take over. Perhaps the wiki should be changed.
If I start ntp-client automatically at boot, it takes about 12 seconds and delays everything which starts after it such as shorewall and local.