You need to go to Chula Vista Branch. Have all the required documents, current EAD, H1-B approval slip(?), I-94, AP, I-485 approval notice, 2 INS pictures etc. The lines are very long before getting a number to be served. My friends went around 7.00 am, got a number around 8:30 am, called to the window to be served around 8:45 am, fingerprinted and stamped in 5 minutes and got out before 9:00 am. They only took their I-94 card, my friends got to keep the 2 EADs, APs etc.
From what I heard, don't go too early, the person that is in charge of fingerprinting and stamping will not be there before 8:00 and sometimes later. If you go around 9:00 am, you might have a long line waiting beore getting a number. Either way you have to wait more than an hour. My friends said best be there before 8:00am. Good luck.