How do I change the resolution timeout?

[Lincoln Yeoh]

Hi,

Say I have BIND configured as a caching nameserver, and for some 
reason the root servers or some other authoritative servers are unreachable.

How do I configure it to "give up" earlier and return a "FAILED/NX" response?

Currently it seems to take 30 seconds before it sends a response, but 
by that time most clients have timed out.

Thanks!
Link.