We are not accredited, so we do not assign credit hours to the students. However, our Charter School partners have given us some advice on this topic. At the Core-Upper level it takes between 30 and 45 hours to complete the 6 week course. This is sufficient time in most states to earn .5 credits per class.
Keep in mind it is up to you as the parent how much you assign them.
Also, keep in mind your local homeschool laws and credit requirements for your state. A great resources is the Homeschool Legal Defense Association's website.