The coin flip sequence will give you the delay you're on guaranteed. You can trust it pretty much with confidence there. The only thing that would affect the IV after that is the frame. So make sure your starting frame is correct and does not vary...ie if you're getting varying results (4 or 5) then it might turn out bad for you when you finally hit your delay only to find out you got the wrong frame. That part is like calibration, it's integral.