Found on SD:
http://slickdeals.net/f/6198374-3-Amazon-Instant-Video-Credit
"You must claim your $3 Amazon Instant Video promotional credit no later than 11:59 p.m. (Pacific Time) on August 6, 2013 or while promotional credits are available. The promotional credit expires at 11:59 p.m. (Pacific Time) on September 6, 2013. The promotional credit may only be used on eligible movie or TV show rentals or purchases from Amazon Instant Video."
http://slickdeals.net/f/6198374-3-Amazon-Instant-Video-Credit
"You must claim your $3 Amazon Instant Video promotional credit no later than 11:59 p.m. (Pacific Time) on August 6, 2013 or while promotional credits are available. The promotional credit expires at 11:59 p.m. (Pacific Time) on September 6, 2013. The promotional credit may only be used on eligible movie or TV show rentals or purchases from Amazon Instant Video."