The minimum time interval between measurement points is not established by the credit requirements. The optimal measurement interval may depend on the system metered and the data storage capacity available. That said, make sure that the intervals between measurement points are short, every 15 minutes or less, to ensure that any spikes in system use are analyzed and addressed immediately. And make sure that these are electronically recorded and relayed back to a computer or BAS, because no manual readings or temporary equipment is allowed.