It can sometimes take up to or over a month to get the results of the blood test back. If the results of the blood test show that the person had a blood alcohol level over the legal limit, they would likely receive a citation in the mail with a court date (their arraignment for the DWI charge).
The State would have the time allowed under North Carolina's statute of limitations to file any formal charge, which isn't likely to have expired by the time the blood results are received.
If the person is found to have had a blood alcohol level over the legal limit and is subsequently charged with DWI, it would be wise to consider consulting a local attorney regarding the circumstances of the blood draw in addition to any other issues that may help in their defense.
In general, the State of North Carolina likely has established statute of limitations based on the level and type of criminal charge. I suggest you contact a lawyer licensed to practice law in NC for more information. Assuming, however, that such limitations are likely calculated in years and not days, your friend may still be charged. Moreover, Blood Alcohol Concentration (BAC) is generally tested by the authorized law enforcement agency for the applicable jurisdiction. Chemical testing takes time and is also impacted by the testing labs work load. Once the lab results are provided to the prosecuting office the defendant will be notified of the charges (assuming a prohibited BAC was found to exist). As such, I would agree that 10 days is not that much time to have passed in light of the fact that the incident involved an accident.
This response is for informational purposes only and is not offered as legal advice.