ECS fieldset for Varnish access logs; time_firstbyte

In the Varnish access logs, there is fieldset **time_firstbyte**
Time from when the request processing starts until the first byte is sent to the client, in seconds. For backend mode: Time from the request was sent to the backend to the entire header had been received.

I looked at the ecs, will it be at [http][request][time_firstbyte] !!