There isn't really an "interview" for PreCheck. You fill in an online form, and then go to an enrollment center, which are at many airports (including SFO - I walked past it yesterday) as well as many locations outside of airports. There you just need to show your ID and have your photo/fingerprints taken, but that's about it. I think they may confirm a few of the details you entered on the form, but it's not what I'd call an interview in any real sense. Appointments are generally available within a few days, or you can just walk-in at most locations.