In the case of the strong parachutes, the manual says regarding time and height that it depends on your speed at deployment.......
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Limited to use by persons up to 115 kg (254 lbs) fully equipped (person, clothes, and equipment except parachute), and up to 150 knots IAS.
Generally, opening times are from 2 to 3 seconds and
the distance fallen would be from 150 feet to 300 feet. This does NOT mean that you should plan on jumping or pulling at 300 feet.
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Plus the time you need to think about jumping or not, time to open door, time to jump and pray.......I guess less than 1000 feet you do not need to pray anymore.....
Best regards,
Miguel