When you request a Steam Key for a title the key will show up below the station you requested it for immediately.
If there are no keys available for the title it will show a "Pending" status below to the station. In the case that the title is out of keys, the content creator will be notified that additional keys are required. Once they are uploaded you will receive an email with the keys that are assigned to your stations.
There is not a set amount of time it takes to receive the keys if more have to be uploaded. It depends on how quickly the content creator uploads the additional keys.
NOTE: Our new content distribution system, which offers one-click titles, does not require Steam Keys. Keys will only be necessary for titles currently not uploaded to our new distribution system. Soon we will no longer be utilizing Steam Keys and you will be able to directly download the content to your computer.