Hi @x86txt ,
2-3 seconds of additional Push Notification time seems like a lot and may be attributed to other factors such as the 2FA device receiving the Push or the application being protected by Duo. Typically the difference between East and West AWS regions is in the milliseconds. For myself (located in the Southwest) I noticed 120ms for East and 96ms for West (http://ec2-reachability.amazonaws.com/).
Has this been proven by logs of the protected application, such as the Authentication Proxy, if used? You might correlate said logs first and timestamp each step of the auth flow as something else might be going on. Either way, I would suggest you contact our Support Team to troubleshoot or request more information regarding our AWS deployment region mapping.
Hope this helps!