coinbase.com buying queue
As far as I can tell the queue itself is not actually functioning. The limit they have only exists for some hours during the day, and at some point they allow you to buy bitcoin and charge it to your bank account. You are then locked in at the rate which you purchased them at, however it takes about 5 days generally to receive your bitcoins. 

I think this happens because they are fronting the money themselves to buy the bitcoins, and have a limited amount of funds per day which they can spare. Each day a new volley of bank transfers comes through and they can then afford to front more for people.