about "query time" (caching)

[Pol Hallen]

Hi all,

I'm struggling about "query time" :-/
Using bind 9.9.5, I configurated it as caching proxy:

dig yahoo.it @192.168.1.212
[...]
96msec

second time:

dig yahoo.it @192.168.1.212
[...]
1msec

seems it works but: if I waiting (ie 5 minutes) and I re-run same 
command, "query time" was increased:

19msec

why? If the record "yahoo.it" is inside cache why after 5 minutes "query 
time" is 19msec?

thanks all for help!

Pol