Temps are 20C/68F. I usually do 14:30, standard agitation. For mixing, I have found it is better to start with only some water in the container, add the washing soda first because it takes the longest to dissolve. I make sure that it does dissolve first, and then I add the Vit C next. The chemical reaction between the soda and the Vit C usually fizzes the water and heats it up a bit, which is why I start with just part of the water (I usually make it a liter at a time, and will develop 6-8 rolls with it). Then I add the coffee and add the rest of the water at a cold enough temperature that it will bring it back down to 20C by the time I hit a liter.