Interruptable As Soon As Frames.
If you want to test this yourself, here's the best way to do it without a hacked Wii:
Enter training mode. It's best if you use a heavy-ish character such as Rob. I have tap jumping disabled, but I doubt it matters. I'm just telling you for the sake of having a control.
It's easiest to see on 1/4 speed, of course. Stand next to your opponent, and use the Paralyzer Shot. Try it a few different times, making note of how fast you can perform an action (other than dtilt, of course) after the animation stops. This is key, because you shouldn't be able to perform an action until the gun is nearly put away.
Next, stand next to your CPU opponent and tap the Paralyzer Shot again. This time, crouch cancel a few frames after the part of the animation in which ZSS suffers a bit of recoil.
You can buffer this slightly. You will notice that when you crouch, the animation of course ends faster (but again, not by a lot) allowing you to act immediately after firing the shot. On heavy characters, try the Usmash. Tilts are also effective. Of course, the question is why you would fire a Paralyzer shot in someone's face, but that isn't necessarily the point.
