I recently had my interview for a reapplication at IAD. IAD does not accept walk ins at all, and they hold a fairly hard line on that.
Some others are relatively easier to do a walk in, as I did at ORD. But - I'd keep checking for a slot that might become available, as GE Zhang increased in size and a walk in is never a sure thing.
1) DO make a placeholder interview farther out; if you do not book an interview within 30 days, iirc, you will have to pay $100 and go through the entire process again.
2) The requirements for the interview include:
- Your passport, driver's licence and any other documentation proving US residence (e.g. your green card)
- A printed copy of your conditional acceptance notification
And the
Practical Travel Safety and Security Issues forum would definitely have been the place to post; there is a lot of helpful information there, and the denizens are pretty knowledgeable. You can request the moderators move this there.