It depends on the time of the year you are hired. If you are hired in the fall, you will automatically be considered seasonal... and if they need castmembers after Christmas, and you and the store are interested, you may be asked to stay on as a permanent CM. Otherwise they do periodically hire permanent CM's during the rest of the year, as needed, and benefits are available after completing orientation... however it may take a while to receive your permanent ID.
Hope this helps!