Please note that this is a limited availability offer -- the promotion isn't being offered to all players. Community Manager Bashiok clarified the nature of the promotion on the official forums yesterday.
However, players are reporting that they have received the promotion without the accompanying email, so you might just have a present waiting for you on your account. To check, log into your Battle.net account, click on your World of Warcraft license, and head to the Referrals & Rewards tab at the bottom of the page. If you have been offered free game time, a link will allow you to activate the game time and apply it to your account. According to the email, the offer expires on November 5 -- so make sure you redeem your game time now, before the offer disappears.