How can I know when my yogurt is ready (in a generic, basic, non-us yogurt maker)? I've bought this yogurt maker (the only one I've been ever able to find in the country I'm living), and it only has a simple on/off button.

Somewhere in the manual, it's written that "Good yogurt takes eight to 15 hours, depending on the type of milk used."

Now I'm wondering how can I know when my yogurt will be ready.

The manual says:


  Preparation of the yogurts
  
  ...
  
  [ yogurt making instructions ]
  
  ...
  
  When the yogurt maker cools off (eight to ten hours after having turned on), make sure that the yogurts have been set. If they haven't, the starter culture did not have enough time to work: start over.


Instructions are really confusing on this point, and it's been something like 15 years since I used a yogurt maker, so I'm not such an expert in yogurt making at home. Does the maker cool off by itself, or do I need to turn it off?
According to http://www.wikihow.com/Make-Yogurt, you can you tell if your yogurt is ready by "gently jiggling one of the containers . . . the yogurt will not move if it is ready and you can take it from the yogurt maker and put it in the refrigerator then. Or you can wait and let it get more tart for 12 hours or more."  It also gives more specific instructions about the three types of yogurt makers, so you can see which one you own and follow more recommendations based on that.