Be advised. It's gonna snow heavily here for the next 2 days (it already started this evening).
If you can afford it, stick with fedex or ups. USPS doesn't really have accountability or reliability in my personal experience.
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(Application done by myself) Date delivered - 8/16/12 Nebraska
Date acceptance letter of application received - 8/20/12
Date of I-797 C Notice of Action (Application Approved) - 8/21/12
Date Biometrics scheduled - 9/12/12
Date of EAD Notification- 9/28/12