I think the answer is yes based on my past 2 EAD's, but the date that the EAD is valid from is usually the day of or the day before you get approval of your EAD... i.e. last time i was approved on 9/20/14 and when i received my EAD the start date was 9/19/14 to 9/18/16.
I figure once i get my approval i will take it back to my job and start working right away.
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Application Sent - 08/15/2012 to Chicago LockboxReceived Date - 08/20/12 Date of I-797 C Notice of Action - 8/23/12, received on 8/27/12 in mail Date of Biometrics Letter - 9/1/12 Appointment - 9/17/12 Biometrics taken 9/17/12 Called FBI 9/22/12 - Bio OK, passed onto USCIS on 9/17/12 I821D Approval 10/18/12 Date of EAD Approval - 10/18/12 EAD Mailed on 10/22/12 EAD Delivered - 10/24/12 Applied for SS 10/25/12 SS Arrived in Mail 11/1/12