Prevent recognizer from recognizing long sentences

Hello,
Is it possible to force stop the recognizer from listening to very long sentences.
I'm trying to recognize orders while the TV is on and the problem is that the recognizer seem to keep listening until there is a silence, which does not occur often on TV, so it ends up recognizing very long sentences, among which my orders are hidden. The result is that the order can only be treated long after it was given.
So is there a way to force the recognizer to stop after a given duration or a given number of words.
Best,
Stanislas