Enable NTP on Ubuntu (with recommended settings for Italy: http://www.inrim.it/ntp/index_i.shtml)

enable-ntp.sh

#!/bin/bash -e
if [[ $EUID -ne 0 ]]; then
   echo "This script has to be executed as root" 1>&2
   exit 1
fi

echo "Installing NTP client..."
rm -rf /var/lib/apt/lists/*
apt-get -y clean
apt-get -y autoclean
apt-get -y update
touch /var/run/utmp
chmod 664 /var/run/utmp
apt-get install -y ntp ntpdate fake-hwclock && \
(sed -i 's/server 0.ubuntu.pool.ntp.org/server ntp1.inrim.it iburst/g' /etc/ntp.conf
sed -i 's/server 1.ubuntu.pool.ntp.org/server ntp2.inrim.it iburst/g' /etc/ntp.conf
sed -i 's/server 2.ubuntu.pool.ntp.org//g' /etc/ntp.conf
sed -i 's/server 3.ubuntu.pool.ntp.org//g' /etc/ntp.conf
sed -i 's/server ntp.ubuntu.com//g' /etc/ntp.conf
timedatectl set-ntp true
/etc/init.d/ntp stop
ntpd -gq
/etc/init.d/ntp start
update-rc.d ntp enable
hwclock -s
ARCH=$(uname -m)
if [ "$ARCH" == "i686" ]; then ARCH="i386"; fi
curl -# -L "http://de.archive.ubuntu.com/ubuntu/pool/universe/n/ntpstat/ntpstat_0.0.0.1-1_$ARCH.deb" -o /tmp/ntpstat.deb
dpkg -i /tmp/ntpstat.deb
echo
echo
echo "NTP client installed! Reboot now to apply the changes.")

To use this script, make sure your box has full internet access and execute:

curl -L http://bit.ly/2tCOiPn | sudo bash

To verify NTP status:

ntpstat

For more information about NTP and how to solve issues, search on Google :)
If the sync is not working, it may be useful to perform a tcpdump:

tcpdump -AAA -vvv -i any port 123

Also check that you have opened port 123 on your firewall.