Can I line up early and possibly walk in?

Yes. Get there as early as you can. It may be just a little wait of course people who make appointments or have appointments are generally first.

You can get there and sign into the virtual queue! I did it yesterday. If the lobby is full, you will wait outside. Unfortunately, I waited in the rain for around 2.5 hours because they don't give you enough notice with their text messaging app to go back to your car. The parking lot behind it is only $3 though.