SFO advice: grabbed two perfect interview slots for Tues Aug 2nd (half an hour apart!) at around midnight last night. One popped up ten minutes after the other so I think it might have been a couple/family who walked in. Twenty minutes before that I saw them add a ton of slots for October weekends that hadn't existed before (although they are now all gone this morning). Then, the July 29 interview I gave up for this reschedule seemed to hang around for longer than I would've expected. So I would suggest checking in around midnight if you're playing the refresh game on the site - less traffic, and based on the other Global Entry thread, I think people might be having successful walk-ins around then because of the shift change.