Good Day,
Except for EAP2 and EAC1 the Performance Periods for each credit must be a minimum of 3 months and a maximum of 2 years. EAP2 and EAC1 must have a full year of data. Performance Periods for each credit do not have to start at the same time, however, they must all end within 30 calender days of each other. See the LEED O+M 2009 rating system addenda from November 2011.