I think it's a myth
If you are in a lift or aircraft that is falling to the ground and you jumped just before hitting the bottom then it would make no difference to your impact speed (and thus nasty jerk and deceleration you will become subject to)
The only thing you will succeed in is accelerating the wreckage \ lift beneath you so it hits the earth slightly harder.
The interesting question is whether it is better to stick with the wreckage or not. I think it is immaterial. Whilst the wreckage IMHO WOULD provide some protection by absorbing the energy of impact it would also be a hinderance as it would add to the impact energies too.
I would rather be away from the aircraft simply for the fact that you stand a change of a soft landing and escape (i.e. into water) instead of being trapped inside some buckled wreckage that later ignites.
Note I'm not a very experienced aviator or analysts, just a simple physicists and so this might all be total rubbish.