I agree with Marcell's comment, though perhaps more from a usability perspective.
Assigning a timeout (as suggested by bažmegakapa) means you're choosing an arbitrary time limit that may or may not fire before the user has processed what they are supposed to do before that time limit is over. Unless your UI somehow makes it clear that they must react within a given time frame, this is likely to lead to frustrated users.
Even taking for granted that the users have had time to process the directions on screen, there's also transition time between moving from keyboard to mouse (or touch, where it's even worse as you have to deal with the UI shifting to hide the soft-keyboard), which means there's even more variance between different users' and their ability to follow the directions before the time limit you've chosen is over.
Just something to think about, in regard to how your interactivity is set up.