I went to Arlington office on Wednesday, October 27th early in the morning around 7am. There were maybe 30 people already waiting in front of the building before me. Normally office opens at 7.30 if I am not mistaken. I was waiting not more than 15 minutes when immigration officer showed up and started asking people if there was anyone having an appointment. He came to me and asked the same question. I said I did not have any appointment and that I came for interim EAD. He told me that everyone has to have an appointment in order get an interim EAD.
On the 90th day, I make an appointment. The earliest day on infopass is 5 days later on Friday, so I make that appointment, and print out the sheet confirmation with the barcode.
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On Friday
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I went to the line at 10:00am for my 10:30 appointment. The guy at the door says you can't come in yet, come back 15 minutes later. That means even if you come really early before your appointment it is pointless. It is best to come 15 min before.