Generally speaking non dairy kefir does ferment faster than regular cow’s milk kefir. (18- 24 hours) It will also depend on temperature in your home and what kind of culture you’re using. If you are using a lot of kefir grains your kefir will ferment faster. It is best to taste it, if it’s sour or tart then it’s done, regardless of how long it has been. The most important thing to realize is that once the sugars are gone then the bacteria has eaten the food out of the milk and it’s time to refrigerate. Longer fermenting times will result in less probiotics, as the bacteria runs out of food to consume.