The weight of your rocket and the altitude all play a factor. If your rocket is moving too fast when the chutte ejects you run the risk of a zipper or a broke shock cord, etc. Or, if your rocket is too close to the ground, it could hit the ground before the ejection. All bad results.
Mark's modified Big daddy (correct me if I'm wrong, Mark) had a 4 second delay on the E. It was perfect. I suggested he use up my E's with the 7 second delay and it was a good thing he said no. On the next 4 second flight I noticed that his Big Daddy would have hit the ground before ejection....
Why don't you tell us about the rocket: Who made it, what model, the weight, the center of gravity. There are plenty of people on this forum who would key in your information into RockSim and tell you what the perfect delay would be.
Disclaimer: This is my opinion only based on observations.