Use the Apple supplied 'ntpdate' commadn and specify a specific time server on the command line.
Must be done under sudo or root.
Of course, Apple doesn't supply man page for it (like so many other system utilities) (Hey, it's a Mac!). Bullshit.
The top of the man page from my Solaris box.
Maintenance Commands ntpdate(1M)
NAME
ntpdate - set the date and time via NTP
SYNOPSIS
/usr/sbin/ntpdate [ -bdosu ] [ -a key# ] [ -e authdelay ]
[ -k keyfile ] [ -m ] [ -o version ] [ -p samples ]
[ -t timeout ] [ -w ] server...
DESCRIPTION
The ntpdate utility sets the local date and time. To deter-
mine the correct time, it polls the Network Time Protocol
servers on the hosts given as arguments. This utility must
be run as root on the local host. It obtains a number of
samples from each of the servers and applies the standard
NTP clock filter and selection algorithms to select the best
of these. Typically, ntpdate can be inserted in the
/etc/rc.local startup up script to set the time of day at
boot time. It can also be run from time-to-time via