Starting from just distilled water, a gallon runs about 24 hours. I always used part of a previous batch to get the time down. I set mine at around 5 on the dial, which would result in CS measuring around 20 uS on a PWT. The Colloid Master is a good unit, and the polarity reversal means the electrodes wear down evenly. But, I would not recommend it for someone who is unable or unwilling to add some kind of stirring mechanism. I think the Silvergen or Silver Puppy are a better choice for non-tinkerers.