Add the use flags to /etc/portage/package.use:
# echo "net-misc/ntp caps" >> /etc/portage/package.use # emerge -av net-misc/ntp
Find a time server that's closest to you, you can find a list of servers here. Once you find a server that you want to use, add it to your /etc/ntpd.conf file
To set the time server when the system shuts down, modify the /etc/conf.d/clock file:
CLOCK_SYSTOHC="yes"
Edit the /etc/conf.d/ntp-client file:
NTPCLIENT_CMD="sntp" NTPCLIENT_OPTS="-P no -r time.server.tld"
Obviously you're going to replace time.server.tld with the server you selected. Next you will need to tell the system to run the ntp-client on boot up:
# rc-update add ntp-client default
To manually run the ntpdate command and set the time run the following command:
# ntpdate -s server