This week Apple’s software head, Craig Federighi, joined the Talk Show podcast to explain and answer questions about Face ID. It’s a great Sunday afternoon listen.
I think my favorite part was the disclosure that if you pick up your iPhone X and swipe from the bottom to the home screen, the iPhone will start the animation while it is simultaneously verifying your face and unlocking the device. There shouldn't be any delay, which is exactly the behavior I would expect.
Before this, I was concerned that you would have to unlock before swiping into your home screen, which would drive me nuts every time I turn the phone on.