From what I've have read online, you can do a walk-in at USCIS in Fresno, CA only after 2 PM. If you go any earlier they will tell you to return later after 2. It also depends how many people they have after 2 pm and who is on staff that day. Just hope that the workers aren't having a bad day.

http://www.visajourney.com/forums/to...nia/?p=4092115

http://www.visajourney.com/forums/to...ion/?p=3190744