2" of letdown. In other words, think about pulling back slowly, and before you get to 2" before full draw, your QAD should be standing at full 90 degrees. But will not be at 90% at say 4" of full draw. You move the cable (or football if you are using it) up and down on the downward cable to adjust this timing.

I have played around with letting it drop fast, like 1" of letoff and making it stay to a vertical position for 3-4", and i find 2" to be sufficient.