Quicksand Hourglasses can be used to finish quests instantly. Hourglasses are activated automatically with the purchase. How many you own and you can use is displayed below a character.   

You can buy single hourglasses in the magic shop.

With a small chance they are offered in packs of ten.

Besides, you can find hourglasses on quests and win them in the game of dice.

During the event "Sands of Time Special" you get ten times the amount: 10 hourglasses instead of 1 and 100 instead of 10.