NOA in 9 days for me
Hello. I mailed out my AOS package with FedEx overnight delivery on Apr 10. It was received by the Chicago lockbox on Apr 11 and the NOA was issued on Apr 17. I received the NOA on Apr 19.
Do you have confirmation of delivery? Were your checks cashed yet? You're waiting a little on the long side, compared to the average of about 10 days. Anyway, if your checks were cashed, I wouldn't be too worried.
Good luck.