For HTTP requests this should be working for you as configured, but this sounds like very long held connections over TLS. Fastly uses a separate tool for terminating TLS in our Points of Presence. This has a hard time out of 60 seconds for connections to ensure that these cannot be exhausted, maintaining a reliable service for all our customers.
If this is affecting all your requests, I'd recommend configuring a failure page for requests which are timing out while you look into the causes. If the slow requests are a limited subset of your requests like report generation, I'd recommend that the could bypass the CDN as reports are commonly user-specific and unlikely to see much benefit of our caching.
If you need a more detailed reply, please contact firstname.lastname@example.org and we can dig into your specific needs.