How to tell when time has been sync'ed with NTP server in Mac OS X Lion?
I'm not sure if there are any log messages by default&mdash;I couldn't find any either.

One possible solution is to just enable logging. You can edit:

/usr/libexec/ntpd-wrapper


And add this (or something similar):

-l /tmp/ntpd.log


To the exec /usr/sbin/ntpd line in the script (the last line). Then kill the ntpd process (it will automatically relaunch) or reboot.

The resulting log looks something like this:

ntpd[10728]: ntpd 4.2.8p6@1.3265 Fri Feb  5 17:38:17 UTC 2016 (124~824): Starting
ntpd[10728]: Command line: /usr/sbin/ntpd -c /private/etc/ntp-restrict.conf -n -g -p /var/run/ntpd.pid -f /var/db/ntp.drift -l /tmp/ntpd.log
ntpd[10728]: proto: precision = 1.000 usec (-20)
ntpd[10728]: proto: fuzz beneath 0.083 usec
ntpd[10728]: Listen and drop on 0 v6wildcard [::]:123
...
ntpd[10728]: drift PPM:0.000 -&gt; -37.418
ntpd[10728]: peer time.asia.apple.com. @ 17.253.66.125
ntpd[10728]: sample offset +0.000000 s @ 17.253.66.125
ntpd[10728]: sample offset -0.000569 s @ 17.253.66.125
ntpd[10728]: sample offset -0.000518 s @ 17.253.66.125