My passport will have to be renewed about 1 year from now. At my interview (several months ago) for GE, the agent said that I would have to bring in my new passport to be updated into the system. When I asked if I had to make an appointment, his response was NO, just come in and it will be taken care of. I hope I won't have to wait one hour.
[When I got my "conditional approval" email, on the day I chose (I went to T4 of JFK), there were no blocked times--I could have chosen any time that day--they were not very busy.
I did a walk-in at ORD and had no porblem.