As a result Quark will be made much faster, but it will taste a little bit more sour, and you have to watch for the temperature. You can used thermos bottles or a yogurt maker to assure the right temperature. I would not recommend to do it on the stove or in the oven, because temperature may vary and kill the bacteria. The bacteria name is Streptococcus cremoris. As a result Quark-making takes longer, but it will taste less sour, and you can make it at room temperature.
Buttermilk is used in Germany for Quark production.
Do not use yogurt thickened with gelatin, because it just will not work. Most fat free yogurts contain gelatin. You might have to go to a health food store. Than higher the percentage, than creamier it will be. This reduces the risk of infection with other organisms.