Login as the root user
Install ntp
# yum -y install ntp

Turn on service:
# chkconfig ntpd on

Synchronize the system clock with 0.pool.ntp.org server:
# ntpdate pool.ntp.org

Start the NTP:
# /etc/init.d/ntpd start

 
Reference:
http://www.cyberciti.biz/faq/howto-install-ntp-to-synchronize-server-clock/