Could you verify that no firewall rules on your system are blocking connections to the IP addresses associated with rdate.cpanel.net?
Code:
host rdate.cpanel.net
rdate.cpanel.net has address 208.74.125.89
rdate.cpanel.net has address 208.74.125.90
rdate.cpanel.net has address 208.74.121.36
rdate.cpanel.net has address 208.74.121.43
Also, check to make sure you have no custom values for the rdate.cpanel.net hostname in your /etc/hosts file.