I see this occasionally as well.
Once the seller has uploaded the tracking number, they (seller/carrier) have 48 hours to pick up/drop off the packet. After that, you may want to consider contacting the seller, to see what the hold up was/is.
If you can't contact the seller, you can contact eBay. Make sure to use the chat funtion, as the people on the other end are eBay employees who have the know-how and power to actually help you.