Sorry. Didn't mean to sound pushy....but I've seen Ryan's Redstone turn in a couple of nice flights.
Shock cord length is one of those things that you almost can't have too much of (as long as it doesn't shorten itself with tangling). You may recall from your first turn at rockets how you'd get dents in nose cones or the tops of body tubes after flights. This is what happens when the shock cord stretches and snaps back, bringing the parts back together quickly. You may see references in discussions to an "Estes dent" or a "smile dent" in a nose cone - and that's a pejorative for what happens when the shock cord isn't long enough to actually absorb the shock of the ejection charge and leads to parts slamming back together again. Having a segment of a circle imprinted in a balsa nose cone by the top of the body tube is what gives a "smile" dent.
Going longer is the easiest way to avoid this damage as long as it doesn't tangle up in the process (and you have room in the model for it). Ejection charges for some motors in particular seem to be rather stronger than they were 40 years ago, too, which exacerbates this problem. So does a heavy nose cone or payload section since, of course, it has more momentum than a light blow-molded plastic or balsa nose cone alone. So if both parts which are attached to the shock cord are relatively massive, longer is again better.
Many of us are happy to see shock cords that are actually long enough to avoid this included in recent Estes kits. It's a small but nice change that has happened in the past few years.
If that new scratch build's nose cone is very light, you might be OK.....but I'd untie the shock cord from the nose cone and put another section of rubber or elastic or even Kevlar in there to make it at least a couple of feet long if at all possible. It's a pretty little model, by the way.