Citrix Federated Authentication Service Integration with APM

I have never needed to add that manually with ADFS. I suspect that there was an error and the ADFS response is indicating the error instead of including an assertion and AuthenticationStatement. BIG-IP might then complain about the missing AuthnInstant, but that's just a symptom of the entire AuthenticationStatement missing. You can look for a StatusCode at the end of the SAML (Use SAML Chrome Panel or Firefox SAML Tracer to see the SAML), it should say success and there should be an assertion, if it's anything else then there is a configuration problem. You can review StatusCode messages here: https://msdn.microsoft.com/en-us/library/hh269642.aspx

Another thing to double check while you're at it is whether the time is in sync between BIG-IP and ADFS.

If you want to try adding the AuthnInstant manually (again, I've never needed this), it might be something like this: Transform: Authentication Time Stamp -> Authentication Time Stamp Transform: Authentication Method -> Authentication Method