RTIME, can be read and set, but not unset.

Available inpassmiss

The between bytes timeout to the backend server.

When requests are relayed from one Fastly cache server to another (as a result of clustering or shielding) the timeout between bytes in effect on those connections is 60 seconds, and cannot be modified.

As a result, if a request is forwarded internally by Fastly before being forwarded to your backend server, the timeout between bytes is capped at 60 seconds.