Why is Cox IMAP email receive slow on a Mac?

I'm using the Cox IMAP account settings on my Macbook Pro running OS X 10.8.4 and I have an iPhone5 setup the same. I receive email (incoming server - imap.cox.net) immediately on my iPhone5, but it takes several minutes upwards to an hour to receive the same email on my Macbook Pro. If I close the Mail app then open it, I get email. Or if I disable the Cox account in Mail and re-enable it I get email. Receiving email from OS X's Mail app while the app is open is slow.

OS X 10.8.4 Mail settings:
Incoming Server: imap.cox.net - port 993 - SSL ON
Outgoing Server: smtp.cox.net - port (Use default 25, 465, 587) - SSL ON 
Check mail every 5 minutes 
Connection Doctor within the OS X Mail app shows everything is working fine. No issues.