FedEx Smartpost tracking numbers are usually 9 digits.
When FedEx has your package you track the FedEx Smartpost package through FedEx tracking and then when the FedEx SmartPost package is handed off to USPS you check the tracking on USPS website.
To check the FedEx Smartpost tracking you add a 92 to the FedEx Smartpost tracking number on USPS website and then you should be able to track the package.
FedEx Smartpost takes so long because the package has to go through FedEx and then through USPS to deliver to you.
Also the FedEx smartpost packages go on trucks that may go way into another state and then come back to your state on indirect routes to deliver the package.
I've had FedEx Smartpost packages go 500 miles away from my location after it's arrived and then come back a few days later.