I tried 14 hours yesterday and it still sort of tastes like milk when I put it in the fridge.
It seems that's the right duration for fridge at around 3-4°C, right into equipment which keeps it at 38°C, and after that right back into the fridge.
2nd batch was just finished, I hope it turned out to be fine as well.
I used 12 drops for 1 liter of milk.