Let you and your body decide.
At about 8 days of brewing, the white tea and green tea jugs are doing really well. Since this is the second time through the brewing cycle, I think all the microbes are fully activated. As mentioned a few posts ago, the yeast is going nuts with the CO2 production. One of my baby SCOBYs has a big 'ol bubble on the underside of it, like one of those goldfish with big bubbles on the cheeks.
Earlier today, I ladled some kombucha from each of the two jugs into a single drinking cup. It's way better than last batch, which was far too sweet and lacking in vinegar and fizz. My apartment is around 62 F, and at day 8, it is still a bit too sweet. The vinegar taste and bubbles are great though. I use a fairly simple test for sugar content. If you've ever had soda, you may know this already... The teeth grind test. My teeth will get sticky with sugar and acid sticking to them, and you should be be able to feel it. As sugar is reduced, this effect subsides.
I also tested my kombucha with some pH paper. I have congo red pH paper which I found on eBay. It reads from 3-5 which is what the range of Kombucha tea should be around. The pH indicated it was around 4, as the paper was partially activated.
I'm guessing 10 days until the kombucha reaches the right balance, since the weather looks crummy and cold in the next few days. Anyway, the one cup a just drank feels real good in my gut. It must be treated as an elixir, as that is precisely what it is... Not for the faint of heart. Lovin' this stuff.
Update: I bottled one jug, the white tea, at 12 days. The green tea I let go to two weeks, as it seemed to be fermenting slower.
I really like the ginger berry flavor, so I mixed a few bottled with it. I'm going to try to let the kombucha gather some fizz for a few days before I crack 'em open.