This video shows a correctly timed QAD.If the rest is fully upright before this,then it is timed incorrectly.It also shows the advantage of the LD models.
http://www.youtube.com/watch?v=PF6Bfm9PwDM
The nock height is critical when using a fallaway.If it is set too low,the arrow can hit the rest and if set to high,it can hit the arm above your rest and slam it into the rest launcher arms.
Also,if the the nock height is wrong,you have an arrow not coming off the bow straight and being pushed either downward or upward causing a very u8nforgiving situation.
Here is a video that shows what a low nocking point can cause and the rest gets the blame for a poorly setup bow.
http://www.youtube.com/watch?v=eZK7O_s1Rq8