You're Touching it Wrong
I’ve seen and heard several reports that the Touch ID is instant. For example John Gruber:
Once you’ve added a fingerprint, subsequent scans of that finger are nearly instantaneous.
While that is technically correct, it’s a misrepresentation of the reality of using Touch ID. Dustin Curtis is accurate here:
When the phone is locked, using Touch ID to unlock is kind of unwieldy; you have to place your finger on the home button sensor, press the button, and then release the button–while still resting your finger on top of it–before Siri activates. It works, but feels strange.
It is only “instant” if the screen is active (awake). I watched multiple new iPhone 5s owners struggle with the initial Touch ID unlock. There’s a perception that the Touch ID both wakes and unlocks the phone by simply placing a finger on the home button.
Touch ID has nothing to do with clicking the button, and there should be almost no delay. … Try this: rest your finger on the home button while the phone is locked. Wake the phone using the power button, not the home button. Instantly unlocked.
Apparently I’ve self-identified with the wrong nerds. Who are these people that unlock their phone with two hands?