USPS tracking does not usually update immediately once the package tracking number has been scanned.
When a USPS worker scans the USPS tracking number it can take a few minutes to as long as 10 to 20 minutes to update the tracking information on the USPS tracking website.
Packages when they are scanned are usually only scanned every 24 hours because packages are on the trucks, planes etc and are not scanned again until they go through another sorting facility.
So checking the USPS tracking too often is a waste of time because there likely will be no updates for 24 hours and the tracking usually doesn't update until around 12:00 AM to 1:00 AM
Also packages that are sent through USPS may not even get scanned at times until it reaches your location which has happened to me.
I've ordered things online and had them shipped to me through USPS and sometimes packages will show shipping label created and then it will not update until it gets to my local post office.
It can be frustrating because it seems that the package was never sent but it's just human error where they may have forgot to scan the package.