Added to the Wiki but: Was in lower Manhattan for a project that finished early. My hotel is just around the corner from the Customs House/1 Bowling Green location but I the CBP website lists them as "by appointment only" -- not having anything better to do I took the train out to JFK to try my luck since the same note wasn't attached to that location.
Walked in, asked CBP officer if they did walk-ins, told me to sign in and it could be an "couple hours or more" because (obviously) they need to handle those with appointments first.
Sat in their little waiting room, started weeding through emails and before I had a chance to get really comfortable was called in... gave the officer my passport, GE card (this was a renewal), he took new fingerprints a new photo and sent me on my way... maybe 20 minutes total from arrival to departure.