Delivery confirmation tracking numbers are sent out to the buyer when the seller generates the label at the post office's website, IIRC. Doesn't mean the package is in the postal system yet, just the tracking number assigned. I've actually had 2 or 3 days go by before I've seen the tracking change to show the package was picked up.
That being said, it usually doesn't show you diddley until the package is delivered, unless it's coming last class/slow boat method. It's meant more for the shipper to prove the package was actually delivered to the recipient, than for the buyer to track the package on it's way to them. And it doesn't require signature either, unless the package is also insured, for over $60 (I think that's the amount). Under that, it can be insured without USPS requiring anyone to sign for it upon delivery. Sadly, I had a package disappear from my mailbox, about 6 years ago now, that tracked as delivered.......but just meant the mailman had stuck it in my mailbox, and then someone came along and helped themselves to my package. :|