How about on your start state, have a get mouse down action, when click is detected go to state2 which has an Int Add (every frame, per second checked) and another get mouse down action that transitions to state3. You could also have a Wait action set to a time you think is too slow for a double click and when that elapses, trigger a transition back to your start state.
then in state3 check the Int value for your given limit.
That's just off the top of my head. If you think about it in logical steps, there are probably a number of different ways of achieving it.