It depends on the double cable release. There is no industry standard. And these thingies are adjustable (that is: one of the two is) to fine tune the delay. So there is no definite answer.
If you have a double cable release, it's easy enough to test. Set up your intended stereo pair, and just try it.
Pressing the thing faster will indeed shorten the delay. But it will also be more violent, increase the risk of shake.