After the 2 1/2 hours, turn off the CrockPot and let it sit for 3 hours. Do not take the lid off. After the 3 hours, scoop out about 2 cups of the milk and pour it into a bowl. Add in 1/2 cup of store-bought plain yogurt with live and active cultures (this is your starter-next time you can use your own homemade starter). Mix well, pour back into the CrockPot, stir, and replace the lid. At this point, I turned my CrockPot to the Warm setting for about 30 minutes, then I turned it back off and unplugged it. That was not in the original instructions, but I got it from a comment on the above mentioned website from someone else who does yogurt a lot. You don't necessarily need to turn it back on. Wrap the CrockPot in a heavy bath towel for insulation, and let it sit for 8 hours (or overnight).
Mine sat for 14 hours because I just let it go overnight. I was surprised at the thickness because I thought it would be very thin. It is pretty comparable to store-bought consistency, maybe a little thinner, though (it thins when you add flavorings in to it).
Now that you have your first yogurt batch, reserve 1/2 cup of your plain yogurt for your "starter" for the next time. Chill your yogurt and enjoy!
If you like thicker yogurt, you can try adding powdered milk or a packet of unflavored gelatin to your original milk mixture, or you can try filtering it at the end. The possibilities are endless!
For $2, you can get a half gallon of tasty, homemade, ingredient-controlled yogurt.