Network Time Protocol is a complex and often over-looked part of configuring systems, but without a trustworthy source of time data, all the logging in the world is essentially worthless. An NTP daemon, creatively named "ntpd", is available via ports, but unfortunately it's missing a patch for the broadcast client (refer to [this post]), so while ports or packages may be the easiest way to install it, you'll be installing a broken port or package.
While not particularly hard, you may not be used to installing stuff from source, so here's the crib notes:
1. Go to the ISC's NTP page and download the latest source code for version 4.2.0 of NTP (anything dated after March 2003 has the fix)
2. Make a directory for it and untar and unzip the file in it:
# mkdir /usr/local/ntp # mv snapshotsntp-4.2.0.tar.gz /usr/local/ntp/ # gunzip sn*.tar.gz # tar xfv snapshotsntp-4.2.0.tar.gz
3. cd into the directory and do the standard install from source (configure, make, make install)
# cd snapshotsntp-4.2.0 # configure (lots of output) # make (a bunch more output) # make install
That's it, you're done with installing from source, what you need to do now is finish Configuring NTP and setup your system to auto-start it when booting (and your system to update itself via ntpdate).