Of course, I had a near-catastrophe with what was apparently an old, weak starter. At five and a half hours, it was still just thick, warm milk, so I checked the temp (110F), added a 1/4 teaspoon of a different strain of dried cultures, stirred, and let it go another three and a half hours, and it set up perfectly! Yogurt crisis averted, leading to a second crisis: Too much yogurt! (Why didn't I make just half a gallon?)
Next, put the liner into a sink of cold water for a few minutes until it comes down to 110F. Scoop out a little of the warm milk into your starter (1/4 cup of prepared yogurt, or I use 1/4 teaspoon of dried starter cultures), then pour this mixture back into the pot along with sweetener of your choice (sugar, honey, maple syrup, stevia, etc--to taste, one half to one cup), and I use about a tablespoon of vanilla bean paste.
Stir well, cover with the lid, and press "yogurt." It will stay warm and do its thing for eight hours, then...it's yogurt! For Greek yogurt, strain through cheesecloth or a flour sack towel, or a special yogurt strainer until it reaches the desired consistency. You might want to whisk it until smooth at this point, and then put it in containers and into the fridge.