I just followed the steps from this article to configure my 2012 DC.
http://support.microsoft.com/kb/816042/en-us
I set it up to use an external time source and used the recommended settings in the article. Event 37 was logged right after restarting the W32time service. It has now been over 24 hours since then and I don't have anymore events being logged. My memory has this event being logged every time it syncs...in my case it should be every 15 minutes. Am I wrong?