Consistency is an issue with parachutes. I am including a link to a design my son followed and set an unofficial record at a Science Olympiad competition. The time stopped when the rocket was no longer visible.
We have had issues with diployment, but this design increased our success to about 80%. Changing the chute material to umbrella material helped tremendously. (Although it is heavy...but if it deploys and there is any wind, it will take off...ours actually went up for some time before leveling off and floating away on the breeze.) We joked that my son was the reason this year's design excluded parachutes.
The design needed quite a bit of modification to be legal for science olympiad. I can send you pictures and video is you need it.