How to validate using the response time of 2 transactions?

This is the transaction I am testing:

1. User sends an HTTP Post
2. Server responds with a redirect
3. Browser follows the redirect
4. Server responds with answer

This shows up as two consecutive requests in NeoLoad. For each, I can validate by giving a maximum response time. However, what I want is to ensure the sum of the two response times must not exceed X seconds. How do I do that? Thanks.