I found the solution on this website. NTPdate was trying to update the date each time an interface went up, which in my case was three times during the boot process. So I modified `/etc/network/if-up.d/ntpdate` to only run `ntpdate` if `eth0` goes up by adding the following to the top of the script:
# Only update the date if eth0 goes up.
if [ "$IFACE" != eth0 ]; then
exit 0
fi