Your game clocks are counted down only, when it is your turn.
 
They do not count down

• when your opponent has to submit the next move
• during your sleeping time
• during your vacation
• on weekends (if you have selected this option in the game invitation)

For a specific game a stopped game-clock is indicated with the following icons shown in the players info section on either the game-page right to the user names, or on the game-info page in the "Off-time"-row:

• : user in sleeping time
  
• : user on vacation
  
• : for weekends