If set up identically to that example, the key will be held down until the speech recognition engine recognizes "over" (note that this may not necessarily be when you say "over").
You can add a "Write a Value to the Event Log" action before the release action to check when the "Wait For Spoken Response" is allowing the command to continue.
Also note that, logically, if you have the "Timeout" value other than 0 set, the action will allow the command to continue after that time (as mentioned in the documentation; Press F1 while VoiceAttack has focus to open VoiceAttackHelp.pdf in your default PDF viewer).
Have you tested this command in-game, or have you opened notepad, executed it, and concluded that it is not working?