Had to drop it from high altitude!

Actually the deployment time is adjustable by shortening the kevlar thread.
I think the knots may have slipped a little over the 5 years or so that this thing has been gathering dust in my garage. I'm pretty sure it was around 2-3 seconds when I was using it.

BTW Matt, I found the best parachute material for this was the plastic from a thin black trash bag, and kevlar thread for the strings. Strings were run all the way across the "canopy" material (crossing at the center/top) and taped in place. Then an appropriate strength of monofilament attached the chute to the back of the tank and that acted as a break-away in case the chute accidentally deployed before the tank was dropped.