obj.ttl
RTIME, can be read and set, but not unset.
Maximum amount of time for which the object will be considered fresh. If the object is not evicted from cache before this time elapses, it will become stale.
This variable is writable only in vcl_hit and vcl_error. Doing so in vcl_error does nothing because error objects are not cacheable. Setting obj.ttl in vcl_hit will only be effective if the value is zero (and will trigger the object to be purged); otherwise, it will retain its existing TTL.
