Just as a thought...sometimes USPS tracking numbers can take a day or two or more to actually enter their system. It may have been shipped on the 10th, but it may not make it into their system until a day or two later. I've had this happen before. Whenever the tracking number makes it into the system it should give information on when it was first received.
I agree with Brian. I have had several occasions recently where the tracking number never was entered into the USPS system or wasn't available for a couple days after the package was actually mailed. So, it could be the seller did as promised.
I would wait until you receive the package and can validate the date stamp. If it was mailed late I would leave a neutral review and an explanation.