Historically, how long does it take for MBP/MBA to reach the refurbished store after release

Aside from the service and other qualitative aspects of dealing directly with Apple, the only "advantage" of purchasing direct from the company is the up to date warranty registration. If you purchase your Apple product through a 3rd party, Apple will have on file an "estimated" purchase date based on the model's manufacturing date.

If you want to claim all of the 365 days on your warranty, you will have to send them the receipt (a scan or picture suffices) in addition to other purchase information so they can update their database to reflect the exact date of purchase.

Other than that, it makes little difference at the end of the day.

If you're pressed for time, and since you mentioned the Macbook Air was new and purchased last week, it probably was installed with OS X Lion which has full-disk encryption. If this assumption is true, then

1. Back up your data. I'd recommend using Time Machine (so you don't have to re-setup your user id, install apps, etc).
2. create another "throwaway" admin id, and log in to your "throwaway" admin id
3. and delete yourself from the Mac using System Preferences -> Users & Groups preference pane.