An hour after taking your turn in a game, you can nudge your opponent. This is located at the very bottom of your main screen (you may have to scroll down by swiping up on the central area of the main screen).

Nudging your opponent will send them a push notification reminding them to take your turn. You can also send another nudge after an hour has passed from the last nudge.

In 24 hours the game will expire. When the game auto-expires when it is the other player's turn, you will get a win if you are leading in the game. If you are tied or losing, the game will go away and it will not count as a loss against you.