You only ferment your kefir for 12 hours? Wow... I've been doing mine for over 48 hours. When I did it 24 hours it still tasted sweet and my body can't tolerate even the slightest bit of sugar or I will break out horribly and have all sorts of problems. I've been making mine super strong. This is only my third batch and I haven't tried it on myself yet because I want to make sure I ferment it to the point there's no sugar left. I gave my first two batches to my boyfriend, but this one that I'm leaving for 2.5 days I'm going to try myself.
Edit-- I just read the part about how you keep the jar covered. See, everywhere I've read says to just cover it with something breathable like cheesecloth so that's what I've been doing. Maybe that's why I need to do mine for 3 days versus your 1 day?
I'm guessing this post is directed towards Chunky? He hasn't logged in for some time, but you could pm him and he'd get an email alert, so that's an option for a specific answer from him. Some factors that could affect the kefir that might allow him to ferment it so fast would be his own personal taste and tolerance, the amount of kefir grains, the amount of milk, and the temperature he's fermenting it in. 6 hours in a warm garage tends to speed things up for my kefir, the one time I did it, the kefir looked like what it'd be in 24 hours at room temperature.