Behold what is likely the fastest 3x3 piston door ever built!
This door uses leaves to create half-tick delay, shaving a full quarter of a second off of the previous record for fastest possible 3x3 door. That may not sound like much, but just try it out and compare, and you'll see how fast and amazing it looks.
There is, of course, a trade off: the door take more space than a more standard design, seeing as they are only 1 block thick nowadays. The above ground part of the door is still only 2 blocks thick, and the part below the floor is 5 or 6 blocks thick.

I include a versions with and without the spiral feature, but who wouldn't want the spiral? It's just so cool! And it helps mask the time between the initial and final retraction. It may or may not be possible to make this door more compact, I don't know, but I'm still really happy with it, and I hope you all enjoy it, too.