Maybe SerialDate() is what you are looking for?
fnInteger8Date($obj.pwdlastset) returns 'yyyy/mm/dd h:mm:ss'
Split(fnInteger8Date($obj.pwdlastset), ' ')[0] returns 'yyyy/mm/dd'
SerialDate(Split(fnInteger8Date($obj.pwdlastset),' ')[0]) returns a number that represents the date