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.

Treibsanduhr der Ungeduld

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

Treibsanduhr der Ungeduld 10er-Paket

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.