Was the property intended to be used 100% for business? Typically, "vacation homes" have personal use as well as rental use.
Regardless, the "business use" begins when you place the property in service as for rental use (i.e., starting the day you would accept a renter or renters). If the property was not available for rental use during that 12-month period, then it would not be considered to be placed in service until that later date.