ntpd will keep your system time current.
If your clock has a large offset, consider using ntpdate $HOST before starting to use ntpd
/etc/ntp.conf
and enter a time server:server time.server.xxx
ntpd
to start at boot by editing /etc/rc.conf
:# ntpd ntpd_enable="YES"
ntpdate
to get the initial clock sync:root@host# ntpdate time.server.xxx
ntpd
:root@host# /etc/rc.d/ntpd start