ARRIVAL TIMES
After reading many reports of SFO's walk-in waiting list being limited to 6 people per day, I erred on the side of caution by arriving at 3 am. It turns out that I could have saved a couple hours, since the next people on the wait list arrived at 5:30am, 5:45am, 6:25am, 6:50am, and 7:00am. That said, I'm glad I got there early for two reasons: (1) I live nearly 2 hours away from SFO, so I was really motivated to avoid returning home empty-handed, and (2) it appears that Sunday mornings might be slower than normal; one of the others had tried on a Saturday morning and was turned away after the list filled up much sooner.

THE WAIT
Staff showed up at 6:45am and began regularly scheduled appointments promptly at 7am after verifying who was there. A few minutes later, they passed around a wait list for up to six walk-ins. As the first on the list, I ended up being called in about 9:15am. The fifth person on the list later reported that the other walk-ins had their names called at 9:35am, 9:50am, 10am, and 10:10am. So, on this particular day, the office managed to get all 6 walk-ins processed within 4 hours of opening the door for scheduled interviews. YMMV.

SECOND SHIFT
Back to the list: once it reached 6 names around 7am, the staff advised subsequent walk-ins to come back around the time of the office's shift change at 3:30pm. This was consistent with some reviews I'd read on another site, including a couple who successfully walked-in the previous Sunday afternoon (they were numbers 3 & 4 on the afternoon list after showing up at 2:45pm, and they had to wait 4 hours for their names to be called.) The key takeaway I got from that report and my experience is that folks can ignore the GE website's posted hours for Sundays at the SFO office (8am - 3:30pm); it looks like they keep the same interview hours every day of the week, at least for the time being.