Was it shipped via Fed-Ex? Or was it just mailed in a box? If it's FedEx and weather conditions are within normal limits, I can't imagine FedEx not being able to give you an exact date that it will arrive, unless in fact the package has been misplaced or delived to the wrong address, which they should still be able to tell you.

If it wasn't sent via FedEx and it was just put in a box and mailed, who knows...

My main concern would be the temperatures. I would expect a healthy snake could probably live a week or more in temps that were between 70 and 80 degrees. if there was a little airflow in the box.