F5 BIG-IP/GTM response AAAA delay

Where was that capture taken - on the client, or on the GTM ?

If it is a WIP you should enable IPv6 NoErrorResponse on the WIP -- this is assuming there is no IPv6 address response available.

https://support.f5.com/kb/en-us/solutions/public/7000/800/sol7851.html

you can apply iRule under listner section

• BIG-IP 12.x and later:
• when DNS_REQUEST {
• if {[DNS::question type] equals "AAAA" }{
•   DNS::header rcode NOERROR
•   DNS::return
•   }  
• }
• BIG-IP 11.6.x and earlier:
• when DNS_REQUEST {
• if { [DNS::rrtype] equals "AAAA" } {
• noerror
• }
• }