Let's use an example so we know we're both on the same page:
John Jacobson has a real life salary of $2.5 million in 2011. In AFB, he is listed as ARB (the year does not matter) for 2012 and 2013. That would mean for 2012 in AFB, he would get a salary of $2.5 million. In 2013 in AFB, he would get whatever salary he received in in real life in 2012.
He may be released at any time without penalty as long as the salary for the remainder of the year is paid. This is only because arbitration contracts are one-year long.