Syncing ESX Server with an external time source

To sync your ESX Server with an external NTP server, do the following at the ESX Server console... Basically you can do the following (replace with the IP Address of an NTP Server.)

Modify the /etc/ntp.conf file as follows:
Under the "# --- OUR TIMESERVERS -----" section create two lines as follows:
restrict mask 255.255.255.255 nomodify notrap noquery
server

Modify the /etc/ntp/step-tickers file and add your NTP Servers, each on their own line, to the file.

Enable the appropriate NTP client ports on the firewall.
/usr/sbin/esxcfg-firewall --enableService ntpClient

Restart the vmware-hostd process.
/sbin/service mgmt-vmware restart

To synchronize the system's time with the NTP server
/usr/sbin/ntpdate -q

To enable the ntp daemon to autostart when the server is rebooted
/sbin/chkconfig --level 345 ntpd on

Start NTP daemon
/sbin/service ntpd start

Set the local hardware clock to the NTP synchronized local system time
/sbin/hwclock --systohc

Ensure the time is accurate
/bin/date