We ship containers from Europe to the US and the only issue we have is we inquire about a container and the shipper gives us date options, vessels, etc and if you don't book/reserve it almost immediately, you'll lose it and end up with a later sailing. The most recent container took less than (4) weeks door-to-door. On the US side, there's two issues - 1) short supply of drivers who deliver the containers from the port to our location and 2) the rail yards only allow 24 hour storage once they arrive at the yard. A year ago, you'd have 3-5 days.
All COSTCO is doing is gaining more control of part of the process. They can still have the same issue many have (though this seems to mostly be an issue on the west coast) and that is the same # 1 I mention above. The linked article refers to this as well.