It is agreed that any loss of damage to the Insured Property arising during any one period of 72 consecutive hours, caused by storm, tempest, flood or earthquake shall be deemed as a single event and therefore to constitute one occurrence with regard to the Excesses provided for herein. For the purpose of the foregoing the commencement of any such 72 hour period shall be decided at the discretion of the Insured it being understood and agreed, however that there shall be no overlapping in any two or more such 72 hour period in the event of damage occurring over a more extended period of time.