Does anyone know for sure if you have to spend $40,000 in any continuous 12 months (like June 2013-May 2014) or $40k from January 1 to December 31 of a year to achieve Hhonors diamond status using the Hilton Surpass Amex?

I've poked around the forum and the Hilton and Amex pages and don't seem to be able to find this information.

Thanks!