Mine took forever, it was stamped approved on September 7 during my interview, however, I did not get it until October 31. I went to infopass appointments three times, and from those experiences and the information I was given, I concluded they had lost my application. Some officers also say that EAD applications may be pending based on some security checks.
Although a District office is not able to grant iEADs anymore, the correct procedure is to take an infopass appointment and talk to the officer about your situation. In my case, the last officer I talked to re-sent an approved application to NBC, a few days later I got my confirmation email and later onmy EAD; what was strange about it is that the dates shown in the EAD card are September 7(valid from) and September 6(expiration).
Good luck to you.