You can look up instant games that are expiring soon by visiting the Games page. Just select the “Only Include Games Ending Soon” button in the Filters drop down menu to view all instant games that are expiring soon. Then click on a game to find details on the last day to redeem in the Prizes section of each Instant Game page.
Alternatively, you can visit the Legal Notices page to find a list of end of game announcements for instant games.