Thank you for your detailed response, Jeremy. I have a similar question to the OP that was not answered.
How can we delay requirement of FaceID when the phone is locked?
There is a setting to do this, but it seems to be disabled for some reason, perhaps a weakness of FaceID.
If you go to: Settings -> Face ID & Passcode -> Require Passcode...you're options are:...."Immediately", if you don't like that option, you are out of luck because it is the only option. It is unclear why they even retained the button to see you have no options.
It would be nice if you just Face-ID'd your phone to authenticate you are the user, to not require authentication again for a few minutes, but I can't find this option or a clear answer in the forums.
Thanks in advance,
Brandon
Oh yeah, I'm using an IphoneX with iOS 11.2.1, currently the most up-to-date distributed version as of 12.24.2017.