Costco's extended shopping hours for its most elite members are taking effect at all its membership clubs this week.  The company began strictly enforcing its new policy on Monday, allowing executive members – its highest and most expensive membership tier – a private, hour-long shopping window during most mornings before the store opens to the rest of its members.Under its new "Executive Member Shopping Hours" policy that began rolling out earlier this summer, more than 37 million shoppers with the $130-pe ...