If you're the member making the reservation by phone they will give you the reservation number immediately upon making it.
If you're making the request online I'm not sure, never did it. Anyone?
If the reservation is placed on the phone, you will see the reservation in your account online immediately. If place via the member website 2 to 3 days. If placed via email 3 to 4 days. The mailed confirmation will take 7 to 10 days.