Yes, they have to cover the same 12 month period. No, they don't have to share the same monthly billing dates.
In order to generate an ENERGY STAR score for a property with a data center, there must be at least one full year of IT energy data and property energy data (they do not have to match exactly, just cover the same 12 month period).
Without at least 12 complete months of IT energy data and property energy consumption data, the property will not be able to receive a score.
However, even if you currently have fewer than 12 complete months of IT energy consumption data, you are encouraged to begin tracking this information in Portfolio Manager so that once you have 12 months, your property will be able to receive a score.