Recommend to unlock this on easy difficulty. If you have trouble, there is a way to slow down the timer (credit to Xenolith666) when you find it difficult to point out next pair, or if you need more time to think about strategy, just press back button to return to menu at once. Then, start the same puzzle, and the game will ask if you want to continue a game from cloud save. Confirm to load, and before you do any move, the timer won't start. In this way, you can have as much time as you want to think!