Those waiting to receive free 30 days of game time from the latest Warcraft promotion event should check their “Gifts” tab in the app to redeem it.

Blizzard is currently sending mail to select players, rewarding them with a free faction change when they invite players back to the game who have been inactive for a while. The recipient receives 30 days of game time entirely free of charge. 

You have one month to redeem the free game time. Otherwise, it will expire.