If you are going to try from scratch, then its just a matter of measuring the time the button is pressed. The Timeri object can do that, and it can release show the value when you depress the button, then it is just a matter of conditions to action depending on length.
With the timeri, you just need to convert your bool trigger from a falling edge to a rising edge when connecting to the stop input. When stop is triggered, it will display a krate value from the green output that represents how many krate samples passed between start and stop.
Maybe this can help you get started..